Add HipChat integration documentation as this was a source of confusion

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 7.9.0 (unreleased)
+  - Add HipChat integration documentation (Stan Hu)
   - Update documentation for object_kind field in Webhook push and tag push Webhooks (Stan Hu)
   - Fix broken email images (Hannes Rosenögger)
   - Fix mass SQL statements on initial push (Hannes Rosenögger)

doc/project_services/hipchat.md

+# Atlassian HipChat
+
+GitLab provides a way to send HipChat notifications upon a number of events,
+such as when a user pushes code, creates a branch or tag, adds a comment, and
+creates a merge request.
+
+## Setup
+
+GitLab requires the use of a HipChat v2 API token to work. v1 tokens are
+not supported at this time. Note the differences between v1 and v2 tokens:
+
+HipChat v1 API (legacy) supports "API Auth Tokens" in the Group API menu. A v1
+token is allowed to send messages to *any* room.
+
+HipChat v2 API has tokens that are can be created using the Integrations tab
+in the Group or Room admin page. By design, these are lightweight tokens that
+allow GitLab to send messages only to *one* room.
+
+### Complete these steps in HipChat:
+
+1. Go to: https://admin.hipchat.com/admin
+1. Click on "Group Admin" -> "Integrations".
+1. Find "Build Your Own!" and click "Create".
+1. Select the desired room, name the integration "GitLab", and click "Create".
+1. In the "Send messages to this room by posting this URL" column, you should
+see a URL in the format:
+
+```
+    https://api.hipchat.com/v2/room/<room>/notification?auth_token=<token>
+```
+
+HipChat is now ready to accept messages from GitLab. Next, set up the HipChat
+service in GitLab.
+
+### Complete these steps in GitLab:
+
+1. Navigate to the project you want to configure for notifications.
+1. Select "Settings" in the top navigation.
+1. Select "Services" in the left navigation.
+1. Click "HipChat".
+1. Select the "Active" checkbox.
+1. Insert the `token` field from the URL into the `Token` field on the Web page.
+1. Insert the `room` field from the URL into the `Room` field on the Web page.
+1. Save or optionally click "Test Settings".
+
+## Troubleshooting
+
+If you do not see notifications, make sure you are using a HipChat v2 API
+token, not a v1 token.
+
+Note that the v2 token is tied to a specific room. If you want to be able to
+specify arbitrary rooms, you can create an API token for a specific user in
+HipChat under "Account settings" and "API access". Use the `XXX` value under
+`auth_token=XXX`.

doc/project_services/project_services.md

@@ -12,7 +12,7 @@ __Project integrations with external services for continuous integration and mor
 - Flowdock
 - Gemnasium
 - GitLab CI
-- HipChat
+- [HipChat](hipchat.md) An Atlassian product for private group chat and instant message.
 - [Irker](irker.md) An IRC gateway to receive messages on repository updates.
 - Pivotal Tracker
 - Pushover