README: document the need of running build-vendor (#1582)
README: document the need of running build-vendor (#1582)

Take the chance to make the list of commands to run locally more uniform.
(In particolar, they are all shell commands now, allowing copy-paste.)
DukeTax/throneteki,cryogen/throneteki,DukeTax/throneteki,ystros/throneteki,cryogen/throneteki