update readme

Author: TamaroWalter

README.md

@@ -3,6 +3,39 @@
 A moodle local plugin that manages the subplugins for the moodle townsquare block.
 Documentation of the townsquare block: https://github.com/learnweb/moodle-local_townsquare
 
+## How to install a subplugin ##
+
+To install a townsquare subplugin, clone the repository of the subplugin into the
+
+`{your/moodle/dirroot}/local/townsquaresupport/townsquareexpansion/{pluginname}
+`
+
+directory.
+
+Afterwards, log in to your Moodle site as an admin and go to _Site administration >
+Notifications_ to complete the installation.
+
+Alternatively, you can run
+
+    $ php admin/cli/upgrade.php
+
+to complete the installation from the command line.
+
+## How to implement a subplugin ##
+
+To implement a subplugin for townsquare, the subplugins needs to meet the following requirements:
+
+1. The plugin type must be`townsquareexpansion_{pluginname}`.
+2. The plugins must have at least the following files:
+
+   - `version.php`
+   - `lang/en/{pluginname}.php `
+   - `classes/{pluginname}.php `
+
+   The most important file is the `{pluginname}` class. This class needs to implement the `townsquaresupportinterface` located in
+   `{your/moodle/dirroot}/local/townsquaresupport/classes/townsquaresupportinterface.php.`. By implementing the interface, the
+   subplugin can make notifications available for the townsquare block.
+
 ## Installing via uploaded ZIP file ##
 
 1. Log in to your Moodle site as an admin and go to _Site administration >