Add development documentation

README.md

@@ -182,3 +182,41 @@ Thanks to all contributors!
 - [FRITZ!Box mit Nagios überwachen](http://blog.gmeiners.net/2013/09/fritzbox-mit-nagios-uberwachen.html)
 - [Fritz!Box and TR-064](http://heise.de/-2550500)
 
+### Development
+
+Fork the project to your GitHub account and commit your changes and please send a pull request. For developing on
+this project it is advantageous to have a Fritz!Box at your place to test out your changes.
+
+Before we start fetching and parsing the TR-064 data we need to know which data
+our Fritz!Box provides. Luckily we can fetch a list of this directly from the
+Fritz!Box. Go to `http://<Your Fritz!Box IP Address>:49000/tr64desc.xml` to
+fetch this list. You will get a XML file that contains many entrys that look
+like the following:
+
+```
+[...]
+<service>
+  serviceType>urn:dslforum-org:service:DeviceInfo:1</serviceType>
+  serviceId>urn:DeviceInfo-com:serviceId:DeviceInfo1</serviceId>
+  controlURL>/upnp/control/deviceinfo</controlURL>
+  eventSubURL>/upnp/control/deviceinfo</eventSubURL>
+  SCPDURL>/deviceinfoSCPD.xml</SCPDURL>
+</service>
+[...]
+```
+To build a TR-064 request we need some information from out choosen entry,
+depending on which information we want to fetch from out Fritz!Box.
+
+| Name         | Description                                                              |
+| ---          | ---                                                                      |
+| service Type | Service category which we want to call                                   |
+| controlURL   | URL we need to call, when fetching information from the choosen category |
+
+We also need some information from the manufacture AVM to build our TR-064
+request. We need to know which _actions_ are available under the choosen
+category, such information we can find inside the [interface documentation from AVM](https://avm.de/service/schnittstellen/).
+On this site you can find a couple of PDF files, which provide an overview about
+the _actions_ we need for the TR-064 request.
+
+Inside the `devel` directory you can find a bash script, that allows you to fetch the raw TR-064 data (basically in  XML
+format).