Move doc/ to the top-level of the repository

[phadej]

No description provided.

[jhrcek]

@phadej This seems to have broken the references in Cabal/Cabal.cabal

I'm getting build errors when building cabal library locally

~/Devel/github.com/haskell/cabal> (cd Cabal; cabal install)
cabal: filepath wildcard 'doc/bugs-and-stability.rst' does not match any
files.

Also these instructions for building users guide no longer work, probably the cd Cabal fixes it.

[phadej]

@jhrcek ok, so you hit an issue #6955 would caught. I took a note.

[phadej]

@jhrcek fixed

[jhrcek]

@phadej Thank you, the (cd Cabal; cabal install) step for building cabal library now works fine for me.

But the build steps for users guide are still broken:
https://github.com/haskell/cabal/blob/master/doc/README.md#how-to-build-it

1. The cd Cabal should probably be removed
2. When I run make users-guide at project's root it basically erases the contents of the doc/buildinfo-fields-reference.rst

It's not blocking me or anything, just wanted to make you aware of the effect this recent move of users guide had.
I'd do the PR myself, but I'm not sure how to fix 2.

[phadej]

@jhrcek that should be fixed now as well. Thanks again for reporting.