Improves Jira integration documentation

changelogs/unreleased/29670-jira-integration-documentation-improvment.yml

+---
+title: Added clarification to the Jira integration documentation.
+merge_request: 10066
+author: Matthew Bender

doc/user/project/integrations/jira.md

@@ -157,6 +157,11 @@ the same goal:
 where `PROJECT-1` is the issue ID of the JIRA project.
+>**Note:**
+- Only commits and merges into the project's default branch (usually **master**) will
+  close an issue in Jira. You can change your projects default branch under
+  [project settings](img/jira_project_settings.png).
+
 ### JIRA issue closing example
 Let's consider the following example: