Include documentation in the application

doc/mailgun.markdown

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+Mailgun
+=======
+
+You can use the service [Mailgun](http://www.mailgun.com/) to create tasks directly by email.
+
+This integration works with the inbound email service of Mailgun (routes).
+Kanboard use a webhook to handle incoming emails.
+
+The [incoming email workflow is described here](create-tasks-by-email.markdown).
+
+Mailgun configuration
+---------------------
+
+Create a new route in the web interface or via the API ([official documentation](https://documentation.mailgun.com/user_manual.html#routes)), here an example:
+
+```
+match_recipient("^kanboard\+(.*)@mydomain.tld$")
+forward("https://mykanboard/?controller=webhook&action=mailgun&token=mytoken")
+```
+
+The Kanboard webhook url is displayed in **Settings > Integrations > Mailgun**
+
+Kanboard configuration
+----------------------
+
+1. Be sure that your users have an email address in their profiles
+2. Assign a project identifier to the desired projects: **Project settings > Edit**
+3. Try to send an email to your project