Prefix branch names with issue numbers

doc/user/project/issues/crosslinking_issues.md

@@ -76,3 +76,10 @@ you can also [set an issue to close automatically](managing_issues.md#closing-is
 as soon as the merge request is merged.
 
 ![issue mentioned in MR](img/mention_in_merge_request.png)
+
+## From branch names
+
+When you create a branch in the same project as an issue and start the branch name with the issue
+number, followed by a hyphen, the issue and MR you create are linked.
+For more information, see
+[Prefix branch names with issue numbers](../repository/branches/index.md#prefix-branch-names-with-issue-numbers).

doc/user/project/repository/branches/index.md

@@ -219,8 +219,13 @@ To change the default pattern for branches created from issues:
 
 ### Prefix branch names with issue numbers
 
-To streamline the creation of merge requests, start your branch name with an
-issue number. GitLab uses the issue number to import data into the merge request:
+To streamline the creation of merge requests, start your Git branch name with the
+issue number, followed by a hyphen.
+For example, to link a branch to issue `#123`, start the branch name with `123-`.
+
+The issue and the branch must be in the same project.
+
+GitLab uses the issue number to import data into the merge request:
 
 - The issue is marked as related to the merge request. The issue and merge request
   display links to each other.