Provide clarification on mirrored repositories for pipelines

doc/ci/pipelines.md

@@ -2,6 +2,11 @@
 > Introduced in GitLab 8.8.
+NOTE: **Note:**
+If you have a [mirrored repository where GitLab pulls from](https://docs.gitlab.com/ee/workflow/repository_mirroring.html#pulling-from-a-remote-repository),
+you may need to enable pipeline triggering in your project's
+**Settings > Repository > Pull from a remote repository > Trigger pipelines for mirror updates**.
+
 ## Pipelines
 A pipeline is a group of [jobs][] that get executed in [stages][](batches).
@@ -121,9 +126,8 @@ The basic requirements is that there are two numbers separated with one of
 the following (you can even use them interchangeably):
 - a space
-- a forward slash (`/`)
+- a slash (`/`)
 - a colon (`:`)
-- a dot (`.`)
 >**Note:**
 More specifically, [it uses][regexp] this regular expression: `\d+[\s:\/\\]+\d+\s*`.

doc/ci/quick_start/README.md

@@ -126,6 +126,11 @@ git push origin master
 Now if you go to the **Pipelines** page you will see that the pipeline is
 pending.
+NOTE: **Note:**
+If you have a [mirrored repository where GitLab pulls from](https://docs.gitlab.com/ee/workflow/repository_mirroring.html#pulling-from-a-remote-repository),
+you may need to enable pipeline triggering in your project's
+**Settings > Repository > Pull from a remote repository > Trigger pipelines for mirror updates**.
+
 You can also go to the **Commits** page and notice the little pause icon next
 to the commit SHA.

doc/ci/yaml/README.md

@@ -10,6 +10,11 @@ of your repository and contains definitions of how your project should be built.
 If you want a quick introduction to GitLab CI, follow our
 [quick start guide](../quick_start/README.md).
+NOTE: **Note:**
+If you have a [mirrored repository where GitLab pulls from](https://docs.gitlab.com/ee/workflow/repository_mirroring.html#pulling-from-a-remote-repository),
+you may need to enable pipeline triggering in your project's
+**Settings > Repository > Pull from a remote repository > Trigger pipelines for mirror updates**.
+
 ## Jobs
 The YAML file defines a set of jobs with constraints stating when they should