Build a working plugin zip

The usual way to get a working version of this plugin, is to headover to the Stud.IP marketplace. If you need your own installable version of the Stud.IP-Opencast-plugin, follow these steps:

1. Check out the plugin to your local machine:
   git clone https://github.com/elan-ev/studip-opencast-plugin.git

2. Make sure you have the latest npm installed then change to the folder studip-opencast-plugin and run:
   npm run zip

3. The production ready zip while will be located in the same folder and look something like
   Opencast-VX.X.zip