gitter import: Add documentation.

templates/zerver/help/import-data-from-gitter.md

@@ -0,0 +1,56 @@
+# Import data from Gitter (beta)
+
+Zulip supports importing data from Gitter, including users, channels,
+messages, attachments, and avatars.
+
+!!! warn ""
+    These instructions require shell access to the Zulip server. If you'd like
+    to import a Gitter organization into the hosted zulipchat.com service,
+    contact support@zulipchat.com.
+
+First, you need to do some things in Gitter to setup the export:
+
+1. [Export your Gitter data](https://github.com/minrk/archive-gitter). You will
+   receive json files of the public rooms that you are a part of.
+   Select the file, `gitter_data.json`, of the room which you want to import to the
+   Zulip server.
+
+    !!! warn ""
+        **Note:** You need the gitter API token to export data. You can get the
+        this token by following the instructions mentioned in the
+        [gitter documentation](https://developer.gitter.im/docs/).
+
+### Import into a new Zulip server
+
+Log in to a shell on your Zulip server as the `zulip` user. Run the
+following commands.
+
+```
+./manage.py convert_gitter_data gitter_data.json --output converted_gitter_data
+./manage.py import --destroy-rebuild-database '' converted_gitter_data
+```
+
+!!! warn ""
+    **Warning:** This will destroy all existing data in your Zulip server
+
+### Import into an existing Zulip server
+
+If you already have some organizations hosted on your Zulip server,
+and want to add import your Gitter data as a new Zulip organization,
+you can use the following procedure.
+
+Log in to your Zulip server as the `zulip` user. Run the following
+commands, replacing `<subdomain>` with the subdomain of the URL
+you'd like for your imported Zulip organization.
+
+```
+./manage.py convert_gitter_data gitter_data.json --output converted_gitter_data
+./manage.py import --destroy-rebuild-database <subdomain> converted_gitter_data
+```
+
+{!import-login.md!}
+
+## Caveats
+
+- [Gitter data export](https://github.com/minrk/archive-gitter) doesn't support
+  the export of the private gitter rooms.

templates/zerver/help/include/sidebar.md

@@ -113,6 +113,7 @@
 * [Update your organization's settings](/help/change-your-organization-settings)
 * [Link to your Zulip from the web](/help/join-zulip-chat-badge)
 * [Import data from Slack](/help/import-data-from-slack)
+* [Import data from Gitter](/help/import-data-from-gitter)
 * [Import or export a Zulip organization](/help/import-or-export-a-zulip-organization)
 * [Restrict new users by email domain](/help/restrict-user-email-addresses-to-certain-domains)
 * [Allow joining without an invitation](/help/allow-anyone-to-join-without-an-invitation)