Improve docs to related merge request API

This adds a number of missing fields from the response.

doc/api/issues.md

@@ -1370,8 +1370,11 @@ Example response:
     "state": "opened",
     "created_at": "2018-09-18T14:36:15.510Z",
     "updated_at": "2018-09-19T07:45:13.089Z",
+    "closed_by": null,
+    "closed_at": null,
     "target_branch": "v2.x",
     "source_branch": "so_long_jquery",
+    "user_notes_count": 9,
     "upvotes": 0,
     "downvotes": 0,
     "author": {
@@ -1411,10 +1414,10 @@ Example response:
     "merge_status": "cannot_be_merged",
     "sha": "3b7b528e9353295c1c125dad281ac5b5deae5f12",
     "merge_commit_sha": null,
-    "user_notes_count": 9,
     "discussion_locked": null,
     "should_remove_source_branch": null,
     "force_remove_source_branch": false,
+    "reference": "!11",
     "web_url": "https://gitlab.example.com/twitter/flight/merge_requests/4",
     "time_stats": {
       "time_estimate": 0,
@@ -1422,7 +1425,67 @@ Example response:
       "human_time_estimate": null,
       "human_total_time_spent": null
     },
-    "squash": false
+    "squash": false,
+    "task_completion_status": {
+      "count": 0,
+      "completed_count": 0
+    },
+    "changes_count": "10",
+    "latest_build_started_at": "2018-12-05T01:16:41.723Z",
+    "latest_build_finished_at": "2018-12-05T02:35:54.046Z",
+    "first_deployed_to_production_at": null,
+    "pipeline": {
+      "id": 38980952,
+      "sha": "81c6a84c7aebd45a1ac2c654aa87f11e32338e0a",
+      "ref": "test-branch",
+      "status": "success",
+      "web_url": "https://gitlab.com/gitlab-org/gitlab/pipelines/38980952"
+    },
+    "head_pipeline": {
+      "id": 38980952,
+      "sha": "81c6a84c7aebd45a1ac2c654aa87f11e32338e0a",
+      "ref": "test-branch",
+      "status": "success",
+      "web_url": "https://gitlab.example.com/twitter/flight/pipelines/38980952",
+      "before_sha": "3c738a37eb23cf4c0ed0d45d6ddde8aad4a8da51",
+      "tag": false,
+      "yaml_errors": null,
+      "user": {
+        "id": 19,
+        "name": "Jody Baumbach",
+        "username": "felipa.kuvalis",
+        "state": "active",
+        "avatar_url": "https://www.gravatar.com/avatar/6541fc75fc4e87e203529bd275fafd07?s=80&d=identicon",
+        "web_url": "https://gitlab.example.com/felipa.kuvalis"
+      },
+      "created_at": "2018-12-05T01:16:13.342Z",
+      "updated_at": "2018-12-05T02:35:54.086Z",
+      "started_at": "2018-12-05T01:16:41.723Z",
+      "finished_at": "2018-12-05T02:35:54.046Z",
+      "committed_at": null,
+      "duration": 4436,
+      "coverage": "46.68",
+      "detailed_status": {
+        "icon": "status_warning",
+        "text": "passed",
+        "label": "passed with warnings",
+        "group": "success-with-warnings",
+        "tooltip": "passed",
+        "has_details": true,
+        "details_path": "/twitter/flight/pipelines/38",
+        "illustration": null,
+        "favicon": "https://gitlab.example.com/assets/ci_favicons/favicon_status_success-8451333011eee8ce9f2ab25dc487fe24a8758c694827a582f17f42b0a90446a2.png"
+      }
+    },
+    "diff_refs": {
+      "base_sha": "d052d768f0126e8cddf80afd8b1eb07f406a3fcb",
+      "head_sha": "81c6a84c7aebd45a1ac2c654aa87f11e32338e0a",
+      "start_sha": "d052d768f0126e8cddf80afd8b1eb07f406a3fcb"
+    },
+    "merge_error": null,
+    "user": {
+      "can_merge": true
+    }
   }
 ]
 ```