Add Issue related Merge Request fix #1144

Author: LeJeanbono

gitlab4j-api/src/main/java/org/gitlab4j/api/IssuesApi.java

@@ -1329,6 +1329,9 @@ public Issue moveIssue(Object projectIdOrPath, Long issueIid, Object toProjectId
 
     /**
      * Get list of merge requests related to an issue.
+     *
+     * <pre><code>GitLab Endpoint: GET /projects/:id/issues/:issue_iid/related_merge_requests</code></pre>
+     *
      * @param projectIdOrPath the project in the form of an Long(ID), String(path), or Project instance
      * @param issueIid the IID of the issue to get the related merge requests for
      * @return a List containing all related merge requests for the specified issue