docs: Add user guide for *Allow anyone to join without an invitation* feature

templates/zerver/help/allow-anyone-to-join-without-an-invitation.md

@@ -0,0 +1,49 @@
+# Allow anyone to join without an invitation
+
+By default, new users can join a Zulip organization with or without an email
+invitation.
+
+However, if you are a realm administrator that wants to limit the membership of
+your organization, you can choose to limit new members to those with email
+invitations.
+
+## Limiting new membership to users invited by organization members
+
+1. Click the cog (![cog](/static/images/help/cog.png)) in the upper right corner
+of the right sidebar.
+
+2. Select **Administration** from the dropdown menu that appears.
+
+    ![Administration dropdown](/static/images/help/administration.png)
+
+3. Upon clicking **Administration**, your view will be replaced with the
+**Administration** page. You will be located on the **Organization settings**
+tab by default.
+
+    ![Administration page](/static/images/help/admin-window.png)
+
+4. In the **Organizations settings** section, locate the **E-mail invitation required**
+checkbox.
+
+    ![Email invitation required](/static/images/help/invite-required.png)
+
+    To limit new members of your organization to those who have been
+    invited to do so, click the **E-mail invitation required** checkbox.
+
+    New users will now require an email invitation sent by a user in your Zulip
+organization to join your organization.
+
+    * If you wish to further limit new membership to your organization, you can
+    select the **Only admins may invite** option that appears when the
+    **E-mail invitation required** option is selected.
+
+        ![Admin invitation](/static/images/help/admin-invite-required.png)
+
+        If this option is enabled, only administrators in your organization can
+    send email invitations to new users.
+
+5. To save any changes you have made to your organization settings, click the
+blue **Save changes** button at the bottom of the **Organizations settings**
+section.
+
+    ![Organization settings Save changes](/static/images/help/organization-settings-save.png)

templates/zerver/help/index.md

@@ -130,7 +130,7 @@ as a “**realm**”.
 ## Organization Settings
 * [Change your organization's name](/help/change-your-organizations-name)
 * Restrict user email addresses to certain domains
-* Allow anyone to join without an invitation
+* [Allow anyone to join without an invitation](/help/allow-anyone-to-join-without-an-invitation)
 * [Only allow admins to invite new users](/help/only-allow-admins-to-invite-new-users)
 * Only allow admins to create new streams
 * [Restrict editing of old messages and topics](/help/restrict-editing-of-old-messages-and-topics)