improvements for "Git Access" page

[Thomas Glanzmann]

Hello everyone,

> https://www.gnupg.org/download/cvs_access.html

I also recently build gnupg myself, I was missing some dependencies
mentioned on this site. I guessed their names and git repositories,
namely:

git://git.gnupg.org/libksba.git
git://git.gnupg.org/libassuan.git
git://git.gnupg.org/libgpg-error.git
git://git.gnupg.org/npth.git
git://git.gnupg.org/gpgme.git

Maybe they should be added to this site as well.

Cheers,
        Thomas