api docs: Use Help Center syntax for restricted endpoints.

templates/zerver/api/create-user.md

@@ -1,8 +1,8 @@
 # Create a user
 
-Create a new user in a realm.
+{!api-admin-only.md!}
 
-**Note**: The requesting user must be an administrator.
+Create a new user account via the API.
 
 `POST {{ api_url }}/v1/users`
 

templates/zerver/api/get-user-groups.md

@@ -1,9 +1,8 @@
 # Get user groups
 
-Fetches all of the user groups in the organization.
+{!api-members-only.md!}
 
-**Note**: Only organization members or admins can contact this
-endpoint; bots and guests cannot contact this endpoint.
+Fetches all of the user groups in the organization.
 
 `GET {{ api_url }}/v1/user_groups`
 

templates/zerver/help/include/api-admin-only.md

@@ -0,0 +1,2 @@
+!!! warn ""
+    This endpoint is only available to organization administrators.

templates/zerver/help/include/api-members-only.md

@@ -0,0 +1,3 @@
+!!! warn ""
+    This endpoint is only available to Members and Administrators;
+    bots and guests cannot use this endpoint.