Move help for renaming group path to docs

And expand on the help text.

app/views/shared/_group_form.html.haml

@@ -22,11 +22,9 @@
     - if @group.persisted?
       .alert.alert-warning.prepend-top-10
-        %ul
-          %li Changing group path can have unintended side effects.
-          %li Renaming group path will rename directory for all related projects
-          %li It will change web url for access group and group projects.
-          %li It will change the git path to repositories under this group.
+        Changing group path can have unintended side effects.
+        = succeed '.' do
+          = link_to 'Learn more', help_page_path('user/group/index', anchor: 'changing-a-groups-path'), target: '_blank'
 .form-group.group-name-holder
   = f.label :name, class: 'control-label' do

doc/user/group/index.md

@@ -188,6 +188,27 @@ Besides giving you the option to edit any settings you've previously
 set when [creating the group](#create-a-new-group), you can also
 access further configurations for your group.
+#### Changing a group's path
+
+> **Note:** If you want to retain ownership over the original namespace and
+protect the URL redirects, then instead of changing a group's path or renaming a
+username, you can create a new group and transfer projects to it.
+
+Changing a group's path can have unintended side effects.
+
+* Existing web URLs for the group and anything under it (i.e. projects) will
+redirect to the new URLs
+* Existing Git remote URLs for projects under the group will no longer work, but
+Git responses will show an error with the new remote URL
+* The original namespace can be claimed again by any group or user, which will
+destroy web redirects and Git remote warnings
+* If you are vacating the path so it can be claimed by another group or user,
+you may need to rename the group name as well since both names and paths must be
+unique
+
+> It is currently not possible to rename a namespace if it contains a
+project with container registry tags, because the project cannot be moved.
+
 #### Enforce 2FA to group members
 Add a security layer to your group by