doc: Add user documentation for set the default streams

Create user documentation for setting the defaul streams
for new users.

templates/zerver/help/index.md

@@ -148,8 +148,8 @@ as a “**realm**”.
 
 ## Streams
 * [Delete a stream](/help/delete-a-stream)
-* Set default streams for new users
-* [Rename a stream](/help/rename-a-stream)
+* [Set default streams for new users](/help/set-default-streams-for-new-users)
+* [Rename a stream](/help/rename-stream)
 * Change a stream's description
 * [Make a public stream private](/help/change-who-can-join-a-stream#make-a-public-stream-private)
 * Add or remove users from a stream

templates/zerver/help/set-default-streams-for-new-users.md

@@ -0,0 +1,30 @@
+# Set default streams for new users
+
+Default streams for an organisation are set by an administrator.
+
+Follow the steps given below to set the default streams for new users
+using an administrator account:
+
+* Click on the cog (![cog](/static/images/help/cog.png)) icon in the
+upper right corner of the sidebar.
+
+* Choose the **Administration** option in the panel shown below:
+
+![admin](/static/images/help/admin.png)
+
+* The **Administration** window will appear like the one below:
+
+![admin window](/static/images/help/admin-window.png)
+
+* Click on the **Default Streams** option as shown below:
+
+![default streams](/static/images/help/default-streams.png)
+
+* To add a stream to **Default Streams**, enter the name of stream
+in the box next to **Stream Name** and press the enter key.
+
+![default stream enter](/static/images/help/default-stream-enter.png)
+
+* To remove a stream from **Default Streams** click on the
+**Remove from default** button next to the name of the stream
+you want to remove.