Tweak desktop instructions (#3069)
Tweak desktop instructions (#3069)

to make it clear you need to do all the things in 'building from
source', including the build-react-sdk dance if you're building
develop.

vector-im/riot-web,martindale/vector,vector-im/riot-web,vector-im/vector-web,martindale/vector,vector-im/vector-web,vector-im/riot-web,vector-im/riot-web,vector-im/vector-web,vector-im/vector-web,vector-im/vector-web,vector-im/riot-web,vector-im/riot-web