Updated readme to help new users get set up without issues

Added more instructions and changed the order of existing instructions. 

The binary distribution of NME from the website includes Haxe 2.1 and Neko 1.8.2, these both need to be upgraded to use NME from source. The upgrade process for haxe as recommended by the haxe website wipes all existing libraries so this should be done first, the libraries are then installed later on.