docs: Add user guide for *Add or invite someone to a stream* feature

templates/zerver/help/add-invite-stream.md

@@ -0,0 +1,38 @@
+# Add or invite someone to a stream
+
+You might want to add a user to a particular stream that they haven't subscribed to yet so that they can send and read messages in that stream. In Zulip, you can add users to a public stream even if you aren't subscribed to that particular stream, but you must be subscribed to a private stream in order to invite a user to join that stream.
+
+You can add users to streams, both public and private, that you're subscribed to.
+
+1. Click the cog (![cog](/static/images/help/cog.png)) next to
+**Streams** in the left sidebar. A tooltip labeled **Subscribe, add, or configure streams**
+will appear upon hovering above the cog.
+
+    ![Browse streams](/static/images/help/streams-1.png)
+2. The stream browser will now appear, showing all streams that you've subscribed to by default. If you wish to see streams that you aren't subscribed to, click the **All Streams** tab; the tab will turn gray upon doing so.
+
+    ![All streams](/static/images/help/all-streams.png)
+3. Locate the stream that you want to add a user to in the stream browser. You can search for specific streams by entering the name of the stream in the **Filter streams** search box.
+
+    ![Filter streams box](/static/images/help/filter-stream.png)
+4. Click on the stream that you want to add someone to. The right side of the stream browser, labeled **Stream settings**, will now display that settings of the stream that you've selected.
+
+    ![Stream selected](/static/images/help/stream-selected.png)
+5. After making sure that your cursor is hovering over the **Streams settings** section (right half of the stream browser), scroll down to the section labeled **Stream membership**. This section shows the usernames and emails of all users that are currently subscribed to the selected stream.
+
+    ![Stream membership](/static/images/help/stream-membership.png)
+6. Click on the box labeled **Email address** and enter the username or email address of the user you want to add to the stream.
+
+    ![Stream membership email](/static/images/help/stream-membership-email.png)
+
+7. As you type, autocompletions will appear. You can choose to select an option from the autocompletion dropdown or fully enter the email address of the user.
+
+    ![Stream membership email autocomplete](/static/images/help/stream-add-email-auto.png)
+
+8. Once the email address is entered in the **Email address**, click the blue **Add** button to add the user to the stream.
+
+    ![Blue add button](/static/images/help/stream-blue-add.png)
+
+9. After you have pressed the blue **Add** button, the user will now be listed in the **Stream membership** section, confirming that they have been successfully added to the stream.
+
+    ![Stream add complete](/static/images/help/stream-add-complete.png)

templates/zerver/help/index.md

@@ -89,7 +89,7 @@ as a “**realm**”.
 * View your current stream subscriptions
 * View messages from a stream
 * The #announce stream
-* Add or invite someone to a stream
+* [Add or invite someone to a stream](/help/add-invite-stream)
 * Change the stream description
 * Rename a stream
 * Preview a stream (not implemented)