Docs: Moved merge requests to word list

doc/development/documentation/styleguide/index.md

@@ -1437,25 +1437,6 @@ It renders on the GitLab documentation site as:
 
 To maintain consistency through GitLab documentation, use these styles and terms.
 
-### Merge requests (MRs)
-
-Merge requests allow you to exchange changes you made to source code and
-collaborate with other people on the same project.
-
-- Use lowercase _merge requests_ regardless of whether referring to the feature
-  or individual merge requests.
-
-As noted in the GitLab [Writing Style Guidelines](https://about.gitlab.com/handbook/communication/#writing-style-guidelines),
-if you use the _MR_ acronym, expand it at least once per document page.
-Typically, the first use would be phrased as _merge request (MR)_ with subsequent
-instances being _MR_.
-
-Examples:
-
-- "We prefer GitLab merge requests".
-- "Open a merge request to fix a broken link".
-- "After you open a merge request (MR), submit your MR for review and approval".
-
 ### Describe UI elements
 
 Follow these styles when you're describing user interface elements in an

doc/development/documentation/styleguide/word_list.md

@@ -123,6 +123,10 @@ Do not use. Options are **primary** or **main**. ([Vale](../testing.md#vale) rul
 
 Do not use first-person singular. Use **you**, **we**, or **us** instead. ([Vale](../testing.md#vale) rule: [`FirstPerson.yml`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/.vale/gitlab/FirstPerson.yml))
 
+## merge requests
+
+Lowercase. If you use **MR** as the acronym, spell it out on first use.
+
 ## Owner
 
 When writing about the Owner role, use a capital "O." Do not use the phrase, "if you are an owner"