Doc : add steps to add a new component

[wadael]

Hi,

The documentation should help users to add more components to the palette

So far, the list of components needs to be completed.
For exemple, I'd like to add the cheap distance sensor HC-SR04, which can be seen in more and more assemblies.

Looks like plugins/fr.obeo.dsl.arduino.design/images/dfrobot is where the pic must be put
and ardublockKit.arduino is the xml file where an entry must be added.

But how do I specify the components connector ? number and name
Thank you