Move to the forge remaining T-compiler docs

[apiraino]

This is moving the last remaining bits of T-compiler documentation to the forge.

I have omitted the documentation about the working groupos because I don't have clear what we prefer to do (WGs as a structure seems that will be sunset in the future). My suggestion would be to migrate documentation about WGs in a follow-up PR. Meanwhile I'll figure out which are active and which are not.

Rendered

r? @davidtwco

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