Add reserved names to docs

doc/gitlab-basics/create-project.md

 # How to create a project in GitLab
 
+>**Notes:**
+- For a list of words that are not allowed to be used as project names see the
+  [reserved names][reserved].
+
 1. In your dashboard, click the green **New project** button or use the plus
    icon in the upper right corner of the navigation bar.
 
@@ -26,3 +30,4 @@
 1. Click **Create project**.
 
 [import it]: ../workflow/importing/README.md
+[reserved]:  ../user/reserved_names.md

doc/user/group/index.md

@@ -57,6 +57,10 @@ By doing so:
 
 ## Create a new group
 
+> **Notes:**
+- For a list of words that are not allowed to be used as group names see the
+  [reserved names][reserved].
+
 You can create a group in GitLab from:
 
 1. The Groups page: expand the left menu, click **Groups**, and click the green button **New group**:
@@ -214,3 +218,4 @@ for the group (GitLab admins only, available in [GitLab Enterprise Edition Start
 
 [permissions]: ../permissions.md#permissions
 [ee]: https://about.gitlab.com/products/
+[reserved]:  ../reserved_names.md

doc/user/group/subgroups/index.md

@@ -83,10 +83,7 @@ structure.
 - You need to be an Owner of a group in order to be able to create
   a subgroup. For more information check the [permissions table][permissions].
 - For a list of words that are not allowed to be used as group names see the
-  [`path_regex.rb` file][reserved] under the `TOP_LEVEL_ROUTES`, `PROJECT_WILDCARD_ROUTES` and `GROUP_ROUTES` lists:
-  - `TOP_LEVEL_ROUTES`: are names that are reserved as usernames or top level groups
-  - `PROJECT_WILDCARD_ROUTES`: are names that are reserved for child groups or projects.
-  - `GROUP_ROUTES`: are names that are reserved for all groups or projects.
+  [reserved names][reserved].
 
 To create a subgroup:
 
@@ -175,5 +172,5 @@ Here's a list of what you can't do with subgroups:
 
 [ce-2772]: https://gitlab.com/gitlab-org/gitlab-ce/issues/2772
 [permissions]: ../../permissions.md#group
-[reserved]:  https://gitlab.com/gitlab-org/gitlab-ce/blob/master/lib/gitlab/path_regex.rb
+[reserved]:  ../../reserved_names.md
 [issue]: https://gitlab.com/gitlab-org/gitlab-ce/issues/30472#note_27747600

doc/user/reserved_names.md

+# Reserved project and group names
+
+Not all project & group names are allowed because they would conflict with
+existing routes used by GitLab.
+
+For a list of words that are not allowed to be used as group or project names, see the
+[`path_regex.rb` file][reserved] under the `TOP_LEVEL_ROUTES`, `PROJECT_WILDCARD_ROUTES` and `GROUP_ROUTES` lists:
+- `TOP_LEVEL_ROUTES`: are names that are reserved as usernames or top level groups
+- `PROJECT_WILDCARD_ROUTES`: are names that are reserved for child groups or projects.
+- `GROUP_ROUTES`: are names that are reserved for all groups or projects.
+
+## Reserved project names
+
+It is currently not possible to create a project with the following names:
+
+- -
+- badges
+- blame
+- blob
+- builds
+- commits
+- create
+- create_dir
+- edit
+- environments/folders
+- files
+- find_file
+- gitlab-lfs/objects
+- info/lfs/objects
+- new
+- preview
+- raw
+- refs
+- tree
+- update
+- wikis
+
+## Reserved group names
+
+Currently the following names are reserved as top level groups:
+
+- 503.html
+- -
+- .well-known
+- 404.html
+- 422.html
+- 500.html
+- 502.html
+- abuse_reports
+- admin
+- api
+- apple-touch-icon-precomposed.png
+- apple-touch-icon.png
+- files
+- assets
+- autocomplete
+- ci
+- dashboard
+- deploy.html
+- explore
+- favicon.ico
+- groups
+- header_logo_dark.png
+- header_logo_light.png
+- health_check
+- help
+- import
+- invites
+- jwt
+- koding
+- notification_settings
+- oauth
+- profile
+- projects
+- public
+- robots.txt
+- s
+- search
+- sent_notifications
+- slash-command-logo.png
+- snippets
+- u
+- unicorn_test
+- unsubscribes
+- uploads
+- users
+
+These group names are unavailable as subgroup names:
+
+- -
+- activity
+- analytics
+- audit_events
+- avatar
+- edit
+- group_members
+- hooks
+- issues
+- labels
+- ldap
+- ldap_group_links
+- merge_requests
+- milestones
+- notification_setting
+- pipeline_quota
+- projects
+- subgroups
+
+[reserved]:  https://gitlab.com/gitlab-org/gitlab-ce/blob/master/lib/gitlab/path_regex.rb