Make clear that notes also serve as comments.

doc/api/README.md

@@ -13,7 +13,7 @@
 + [Merge Requests](merge_requests.md)
 + [Issues](issues.md)
 + [Milestones](milestones.md)
-+ [Notes](notes.md)
++ [Notes](notes.md) (comments)
 + [Deploy Keys](deploy_keys.md)
 + [System Hooks](system_hooks.md)
 + [Groups](groups.md)

doc/api/issues.md

@@ -193,3 +193,7 @@ Parameters:
 
 + `id` (required) - The project ID
 + `issue_id` (required) - The ID of the issue
+
+## Comments on issues
+
+Comments are done via the notes resource.

doc/api/merge_requests.md

@@ -258,3 +258,7 @@ Parameters:
   }
 ]
 ```
+
+## Comments on issues
+
+Comments are done via the notes resource.

doc/api/notes.md

+Notes can be wall notes or comments on snippets, issues or merge requests.
+
 ## Wall
 
 ### List project wall notes