integrations: Add discourse integration.

The actual integration lives on the Discourse side.

templates/zerver/integrations/discourse.md

@@ -0,0 +1,21 @@
+On your {{ settings_html|safe }},
+[create a bot](/help/add-a-bot-or-integration) for
+{{ integration_display_name }}. Make sure that you select
+**Incoming webhook** as the **Bot type**:
+
+![](/static/images/help/bot_types.png)
+
+The API keys for "Incoming webhook" bots are limited to only
+sending messages via webhooks. Thus, this bot type lessens
+the security risks associated with exposing the bot's API
+key to third-party services.
+
+Copy the `USERNAME` and `API KEY` - you'll need it later.
+
+Head over to the
+[Discourse Chat Integration Setup Instructions](https://meta.discourse.org/t/68501)
+and complete them.
+
+{!congrats.md!}
+
+![](/static/images/integrations/discourse/001.png)

zerver/lib/integrations.py

@@ -315,6 +315,8 @@ INTEGRATIONS = {
     ),
     'codebase': Integration('codebase', 'codebase', ['version-control'],
                             doc='zerver/integrations/codebase.md'),
+    'discourse': Integration('discourse', 'discourse', ['communication'],
+                             doc='zerver/integrations/discourse.md'),
     'email': EmailIntegration('email', 'email', ['communication'],
                               doc='zerver/integrations/email.md'),
     'git': Integration('git', 'git', ['version-control'], doc='zerver/integrations/git.md'),