Merge branch 'doc-custom-githook-ui' into 'master'

Document custom Git hook error message

## What does this MR do?

Documents new functionality introduced by https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5073

## Does this MR meet the acceptance criteria?

- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5088

doc/README.md

@@ -23,7 +23,7 @@
 - [Authentication/Authorization](administration/auth/README.md) Configure
   external authentication with LDAP, SAML, CAS and additional Omniauth providers.
-- [Custom git hooks](hooks/custom_hooks.md) Custom git hooks (on the filesystem) for when webhooks aren't enough.
+- [Custom Git hooks](administration/custom_hooks.md) Custom Git hooks (on the filesystem) for when webhooks aren't enough.
 - [Install](install/README.md) Requirements, directory structures and installation from source.
 - [Restart GitLab](administration/restart_gitlab.md) Learn how to restart GitLab and its components.
 - [Integration](integration/README.md) How to integrate with systems such as JIRA, Redmine, Twitter.

doc/administration/custom_hooks.md

+# Custom Git Hooks
+
+>
+**Note:** Custom Git hooks must be configured on the filesystem of the GitLab
+server. Only GitLab server administrators will be able to complete these tasks.
+Please explore [webhooks](../web_hooks/web_hooks.md) as an option if you do not
+have filesystem access. For a user configurable Git hook interface, please see
+[GitLab Enterprise Edition Git Hooks](http://docs.gitlab.com/ee/git_hooks/git_hooks.html).
+
+Git natively supports hooks that are executed on different actions.
+Examples of server-side git hooks include pre-receive, post-receive, and update.
+See [Git SCM Server-Side Hooks][hooks] for more information about each hook type.
+
+As of gitlab-shell version 2.2.0 (which requires GitLab 7.5+), GitLab
+administrators can add custom git hooks to any GitLab project.
+
+## Setup
+
+Normally, Git hooks are placed in the repository or project's `hooks` directory.
+GitLab creates a symlink from each project's `hooks` directory to the
+gitlab-shell `hooks` directory for ease of maintenance between gitlab-shell
+upgrades. As such, custom hooks are implemented a little differently. Behavior
+is exactly the same once the hook is created, though.
+
+Follow the steps below to set up a custom hook:
+
+1. Pick a project that needs a custom Git hook.
+1. On the GitLab server, navigate to the project's repository directory.
+   For an installation from source the path is usually
+   `/home/git/repositories/<group>/<project>.git`. For Omnibus installs the path is
+   usually `/var/opt/gitlab/git-data/repositories/<group>/<project>.git`.
+1. Create a new directory in this location called `custom_hooks`.
+1. Inside the new `custom_hooks` directory, create a file with a name matching
+   the hook type. For a pre-receive hook the file name should be `pre-receive`
+   with no extension.
+1. Make the hook file executable and make sure it's owned by git.
+1. Write the code to make the Git hook function as expected. Hooks can be
+   in any language. Ensure the 'shebang' at the top properly reflects the language
+   type. For example, if the script is in Ruby the shebang will probably be
+   `#!/usr/bin/env ruby`.
+
+That's it! Assuming the hook code is properly implemented the hook will fire
+as appropriate.
+
+## Custom error messages
+
+>**Note:**
+This feature was [introduced][5073] in GitLab 8.10.
+
+If the commit is declined or an error occurs during the Git hook check,
+the STDERR and/or SDOUT message of the hook will be present in GitLab's UI.
+
+![Custom message from custom Git hook](img/custom_hooks_error_msg.png)
+
+[hooks]: https://git-scm.com/book/en/v2/Customizing-Git-Git-Hooks#Server-Side-Hooks
+[5073]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5073

doc/hooks/custom_hooks.md

 # Custom Git Hooks
-**Note: Custom git hooks must be configured on the filesystem of the GitLab
-server. Only GitLab server administrators will be able to complete these tasks.
-Please explore [webhooks](../web_hooks/web_hooks.md) as an option if you do not have filesystem access. For a user configurable Git Hooks interface, please see [GitLab Enterprise Edition Git Hooks](http://docs.gitlab.com/ee/git_hooks/git_hooks.html).**
-
-Git natively supports hooks that are executed on different actions.
-Examples of server-side git hooks include pre-receive, post-receive, and update.
-See
-[Git SCM Server-Side Hooks](https://git-scm.com/book/en/v2/Customizing-Git-Git-Hooks#Server-Side-Hooks)
-for more information about each hook type.
-
-As of gitlab-shell version 2.2.0 (which requires GitLab 7.5+), GitLab
-administrators can add custom git hooks to any GitLab project.
-
-## Setup
-
-Normally, git hooks are placed in the repository or project's `hooks` directory.
-GitLab creates a symlink from each project's `hooks` directory to the
-gitlab-shell `hooks` directory for ease of maintenance between gitlab-shell
-upgrades. As such, custom hooks are implemented a little differently. Behavior
-is exactly the same once the hook is created, though. Follow these steps to
-set up a custom hook.
-
-1. Pick a project that needs a custom git hook.
-1. On the GitLab server, navigate to the project's repository directory.
-For an installation from source the path is usually
-`/home/git/repositories/<group>/<project>.git`. For Omnibus installs the path is
-usually `/var/opt/gitlab/git-data/repositories/<group>/<project>.git`.
-1. Create a new directory in this location called `custom_hooks`.
-1. Inside the new `custom_hooks` directory, create a file with a name matching
-the hook type. For a pre-receive hook the file name should be `pre-receive` with
-no extension.
-1. Make the hook file executable and make sure it's owned by git.
-1. Write the code to make the git hook function as expected. Hooks can be
-in any language. Ensure the 'shebang' at the top properly reflects the language
-type. For example, if the script is in Ruby the shebang will probably be
-`#!/usr/bin/env ruby`.
-
-That's it! Assuming the hook code is properly implemented the hook will fire
-as appropriate.
+This document was moved to [administration/custom_hooks.md](../administration/custom_hooks.md).