[Wiki] Add documentation for running games on the built engine.

[EternallyEmber]

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People need to know how to run games on the built engine, what's the point besides learning anyways then.

[EternallyEmber]

is it as simple as dragging the hl2/tf/csgo/cs/l4d/l4d2 folder to the built engine folder? or is extra editing of text files needed. like 'gameinfo.txt'

[AruMoon]

Specify --prefix parameter at ./waf configure step to your game folder and then just use ./waf install

[cafalchio]

It is not clear how to run