Documentation could use some updates regarding dependencies

[Migaroez]

I install most Umbraco packages trough Nuget . Matt explained to me why there is no dependency tracking in the Nuget package. Which is fine, to bad it took me so long to figure out why i couldn't build my project anymore.

Please add the Json/Umbraco dependency to the install instructions and/or add the Nuget missing dependency thing under known issues.