Nim: TinyC is not documented

[juancarlospaco]

TinyC support is not documented, is builtin but Disabled by default, it prints an error and quit,
but the Nim manual dont explain how to enable TinyC, for users of the language.

I know how to manually git clone and pass compile params and manually build,
but I want Nim with TinyC support with the vanilla standard choosenim tooling,
I know that adding -d:tinyc somewhere on a *.cfg file probably will make choosenim install with TinyC support,
but I dont know how to do it, is not documented,
being a builtin feature it should be documented for v1.0.

I know is not better than the default target, but is like an intermediate step between NimScript and C targets.

If you quickly comment how to properly enable it with choosenim and vanilla tooling, I can send a Documentation PR.

:slightly_smiling_face:

[Araq]

I found TinyC to be unreliable on various OSes so I don't want to document it. We need fewer half-assed features in Nim. ;-)