Add unmentioned commands to the docs.

[philderbeast]

The docs claim to "give an in-depth description of all the commands" but this isn't so.

Doing a quick check, it looks like commands fetch, info, list, user-config, upload, check, get, hscolour and report are not discussed. The init command is discussed in the quickstart of developing-packages.rst so maybe we should link to it? Same goes for the outdated and gen-bounds commands that are discussed in cabal-package.rst.

I see that hscolour is deprecated. Should we move it alongside the v1 stuff (as a separate issue and PR)?

$ cabal help hscolour
Generate HsColour colourised code, in HTML format.

Usage: cabal hscolour [FLAGS]

Requires the hscolour program.

Deprecated in favour of 'cabal haddock --hyperlink-source'.

Originally posted by @philderbeast in #7964 (comment)