Created Notify_mattermost (markdown)

Notify_mattermost.md

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+## Mattermost Notifications
+* **Source**: https://mattermost.com/
+* **Icon Support**: Yes
+* **Message Format**: Text
+* **Message Limit**: 4000 Characters per message
+
+To use this plugin, you need to first set yourself up with http://mattermost.com. Download their software and set it up. The setup is based on Incoming Web Hooks requiring you to generate your own WebHook ID.
+
+### Syntax
+Valid syntaxes are as follows:
+* **mmost**:://**{hostname}**/**{webhook_id}**
+* **mmost**:://**{hostname}**:**{port}**/**{webhook_id}**
+* **mmosts**:://**{hostname}**/**{webhook_id}**
+* **mmosts**:://**{hostname}**:**{port}**/**{webhook_id}**
+
+Secure connections (via https) should be referenced using **mmosts://** where as insecure connections (via http) should be referenced via **mmost://**.
+
+### Parameter Breakdown
+| Variable    | Required | Description
+| ----------- | -------- | -----------
+| hostname    | Yes      | The server Mattermost is listening on.
+| webhook_id  | Yes      | The WebHook ID you would have gotten after setting up the Mattermost server
+| port        | No       | The server port Mattermost is listening on. By default the port is **8065**.
+
+#### Example
+Send a secure Mattermost notification to our server
+```bash
+# Assuming our {hostname} is mattermost.server.local
+# Assuming our {webhook_id} is 1234ABCD5678
+
+notify.py mmosts://mattermost.server.local/1234ABCD5678
+```