Added instructions on howto install extra modules

MagicMirror²-Modules.md

@@ -9,9 +9,28 @@ The following modules are installed by default.
 - [**Hello World**](https://github.com/MichMich/MagicMirror/tree/v2-beta/modules/default/helloworld)
 - [**Alert**](https://github.com/MichMich/MagicMirror/tree/v2-beta/modules/default/alert)
 
+##Optional Modules:
+##Installing:
+To install 3rd party or your own custom modules just follow these steps:
+- Navigate to the modules folder via the follow command: `cd ~/MagicMirror/modules`.
+- Clone the module from github: `git clone https://github.com/author/module-name` (remembering to replace the URL with that of the module on github).
+- Follow any additional instruction on from the modules readme.
+- Add your brand new module to your config! This is the file `config/config.js` that you duplicated earlier. Edit this in your favourite editor and add:
+    
+    ```
+    {
+        module: 'module name',
+        position: 'position',
+        header: 'optional header',
+        config: {
+            extra option: 'value'
+        }
+    },
+    ```
+    to the list of modules. You can look at the default modules for examples and further details can be found on the main readme.
+
 ##3rd party modules:
 The following modules are created by their respective authors:
-
 - **[MMM-FRITZ-Box-Callmonitor by PaViRo](https://github.com/paviro/MMM-FRITZ-Box-Callmonitor)** <br> FRITZ!Box Callmonitor (Display an alert when someone is calling and offers a call history...)
 
 - **[MMM-Callmonitor-Current-Call by PaViRo](https://github.com/paviro/MMM-Callmonitor-Current-Call)** <br> Extension for [MMM-FRITZ-Box-Callmonitor](https://github.com/paviro/MMM-FRITZ-Box-Callmonitor) (Displays the currently active call)