Add install instructions

Author: matt

INSTALL.md

@@ -0,0 +1,19 @@
+## Installation
+
+These instructions assume you installed FreeScout using the [recommended process](https://github.com/freescout-helpdesk/freescout/wiki/Installation-Guide), the "one-click install" or the "interactive installation bash-script", and you are viewing this page using a macOS or Ubuntu system.
+
+Other installations are possible, but not supported here.
+
+1. Download the [latest release of UnSub](https://github.com/aarhus/unsub).
+
+2. Unzip the file and then place the unzipped folder in the Modules directory in the web root (i.e. /var/www/html/Modules/ )
+
+3. Make sure that the files are readable by the webserver....
+
+   ```sh
+   chown -r www-data:www-data /var/www/html/Modules/UnSub/
+   ```
+
+4. Access your admin modules page like https://freescout.example.com/modules/list.
+
+5. Find **Aarhus Unsub** and click ACTIVATE.