Consolidated duplicate guidelines for libraries

Because they were duplicated

Related to: https://gitlab.com/gitlab-org/technical-writing/-/issues/744

doc/development/contributing/index.md

@@ -107,20 +107,6 @@ your code has multiple disciplines, you may mention multiple merge request coach
 GitLab receives a lot of community contributions. If your code has not been reviewed within two
 working days of its initial submission, you can ask for help with `@gitlab-bot help`.
 
-#### Addition of external libraries
-
-When submitting code to GitLab, you may feel that your contribution requires the aid of an external
-library. If your code includes an external library, please provide a link to the library, as well as
-reasons for including it.
-
-Mention a maintainer in merge requests that contain:
-
-- More than 500 changes.
-- Any major [breaking changes](../deprecation_guidelines/index.md).
-- External libraries.
-
-If you are not sure who to mention, the reviewer will do this for you early in the merge request process.
-
 #### Issues workflow
 
 This [documentation](issue_workflow.md) outlines the current issue workflow:

doc/development/contributing/merge_request_workflow.md

@@ -190,7 +190,11 @@ Example commit message template that can be used on your machine that embodies t
 To make sure that your merge request can be approved, please ensure that it meets
 the contribution acceptance criteria below:
 
-1. The change is as small as possible.
+1. The change is as small as possible. 
+1. If the merge request contains more than 500 changes:
+   - Explain the reason
+   - Mention a maintainer
+1. Mention any major [breaking changes](../deprecation_guidelines/index.md).
 1. Include proper tests and make all tests pass (unless it contains a test
    exposing a bug in existing code). Every new class should have corresponding
    unit tests, even if the class is exercised at a higher level, such as a feature test.