Add missing version notes to resource events API pages

doc/api/issues.md

@@ -1772,3 +1772,8 @@ Example response:
   "akismet_submitted": false
 }
 ```
+
+## List issue state events
+
+To track which state was set, who did it, and when it happened, check out
+[Resource state events API](./resource_state_events.md#issues).

doc/api/merge_requests.md

@@ -2449,3 +2449,8 @@ Example response:
 ## Approvals **(STARTER)**
 
 For approvals, please see [Merge Request Approvals](merge_request_approvals.md)
+
+## List merge request state events
+
+To track which state was set, who did it, and when it happened, check out
+[Resource state events API](./resource_state_events.md#merge-requests).

doc/api/resource_milestone_events.md

@@ -6,6 +6,8 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 
 # Resource milestone events API
 
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/31720) in GitLab 13.1.
+
 Resource milestone events keep track of what happens to GitLab [issues](../user/project/issues/) and
 [merge requests](../user/project/merge_requests/).
 

doc/api/resource_state_events.md

@@ -6,6 +6,8 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 
 # Resource state events API
 
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/35210/) in GitLab 13.2.
+
 Resource state events keep track of what happens to GitLab [issues](../user/project/issues/) and
 [merge requests](../user/project/merge_requests/).
 

doc/api/resource_weight_events.md

@@ -6,6 +6,8 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 
 # Resource weight events API
 
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/32542) in GitLab 13.2.
+
 Resource weight events keep track of what happens to GitLab [issues](../user/project/issues/).
 
 Use them to track which weight was set, who did it, and when it happened.