C#: Add module README
C#: Add module README

This should clarify development workflow with the NuGet packages.

Shockblast/godot,akien-mga/godot,josempans/godot,godotengine/godot,josempans/godot,vkbsb/godot,firefly2442/godot,vkbsb/godot,vkbsb/godot,BastiaanOlij/godot,guilhermefelipecgs/godot,godotengine/godot,Zylann/godot,pkowal1982/godot,sanikoyes/godot,akien-mga/godot,Shockblast/godot,vkbsb/godot,godotengine/godot,firefly2442/godot,ZuBsPaCe/godot,sanikoyes/godot,guilhermefelipecgs/godot,godotengine/godot,BastiaanOlij/godot,vkbsb/godot,firefly2442/godot,pkowal1982/godot,josempans/godot,guilhermefelipecgs/godot,BastiaanOlij/godot,Shockblast/godot,akien-mga/godot,josempans/godot,guilhermefelipecgs/godot,Zylann/godot,godotengine/godot,akien-mga/godot,godotengine/godot,firefly2442/godot,akien-mga/godot,firefly2442/godot,ZuBsPaCe/godot,pkowal1982/godot,Zylann/godot,guilhermefelipecgs/godot,Zylann/godot,Shockblast/godot,pkowal1982/godot,akien-mga/godot,ZuBsPaCe/godot,BastiaanOlij/godot,Shockblast/godot,godotengine/godot,Zylann/godot,Zylann/godot,sanikoyes/godot,guilhermefelipecgs/godot,sanikoyes/godot,guilhermefelipecgs/godot,pkowal1982/godot,sanikoyes/godot,sanikoyes/godot,BastiaanOlij/godot,Shockblast/godot,Shockblast/godot,vkbsb/godot,Zylann/godot,ZuBsPaCe/godot,josempans/godot,BastiaanOlij/godot,ZuBsPaCe/godot,godotengine/godot,Shockblast/godot,vkbsb/godot,firefly2442/godot,BastiaanOlij/godot,akien-mga/godot,BastiaanOlij/godot,vkbsb/godot,josempans/godot,akien-mga/godot,pkowal1982/godot,josempans/godot,ZuBsPaCe/godot,sanikoyes/godot,pkowal1982/godot,ZuBsPaCe/godot,guilhermefelipecgs/godot,sanikoyes/godot,Zylann/godot,ZuBsPaCe/godot,pkowal1982/godot,firefly2442/godot,firefly2442/godot,josempans/godot