[gnu elpa] Adding disk.el

Hello.

A few weeks ago I sent an Emacs patch for adding =disk.el= to the
upstream Emacs dist, since it didn't get accepted, I am now submitting
it as part of GNU Elpa.

disk.el provides an indent-tabs-mode interface to block devices, plus a
couple commands to manipulate them.

Repo is on SourceHut: https://git.sr.ht/~rosell/disk.el

Since this is my first Elpa package, please tell me if I did something
wrong...

Thanks in advance.

-- 
- mario