Updating Readme with more detailed instructions.

Hello luc!  I'm a software engineer working on getting your latest source running on my printer.  It has been pretty tricky trying to cobble together all the needed information, so I figured I would make my first contribution cleaning up and extending your current documentation.  I would eventually like to collaborate by sending future pull requests for you to update your repo as the definitive source if that is ok with you.  I still need to calibrate my X, Y, Z axis and extruder before I can get my first test print out.  I feel like I am pretty close at this point though.
Do you know there is an helper on maintenance menu of printer for this with all explaination ?
it is called manual leveling in menu