Add "Close topic" to "Moderator Instructions"

Author: per1234

content/categories/staff/moderation/_topics/moderator-instructions/1.md

@@ -33,6 +33,7 @@ For an overview of the Discourse moderation system, see the "[**Discourse Modera
   - [Reopen auto-closed topic](#reopen-auto-closed-topic)
 - [General](#general)
   - [Move topic to correct category](#move-topic-to-correct-category)
+  - [Close topic](#close-topic)
   - [Delete post](#delete-post)
   - [Delete topic](#delete-topic)
   - [Investigate user](#investigate-user)
@@ -515,6 +516,18 @@ Users often create topics in [categories](https://forum.arduino.cc/categories) w
 
 ---
 
+<a name="close-topic"></a>
+
+### [Close topic](#close-topic)
+
+Closing a topic will prevent any further replies by non-staff users.
+
+1. Click the wrench button at the bottom of the topic.
+   A menu will open.
+1. Select "**Close Topic**" from the menu.
+
+---
+
 <a name="delete-post"></a>
 
 ### [Delete post](#delete-post)