channels make everything more stateful, and therefore more complicated
and potentially confusing, but aren't needed for this task, so don't encourage their use.
e.g. nix-env -e subversion => nix-env --uninstall subversion
The aim is to make the documentation less cryptic for newcomers and the
long options are more self-documenting.
The change was made with the following script:
<https://github.com/aschmolck/convert-short-nix-opts-to-long-ones>
and sanity checked visually.
