We need a guide on building the engine and running a game locally

Currently we only have 2 very old guides ported from wiki.

Instead we should provide information on how to build the engine using the docker-v2 method and running a completely sandboxed environment using some vanilla game, suggestion being vroomrts via local filesystem.

Start by reviewing the two existing guides ported from the wiki and the docker-v2 build method. Document building the engine, then running a completely sandboxed environment with a vanilla game such as vroomrts from the local filesystem; done means a newcomer can follow the guide from build through local game launch.

Written by the indexing model from the issue text.