Update README's Debian install instructions

[Captain-Barge]

Change

This PR changes the README's Debian install instructions. It removes the existing link to the unstable Debian package, and replaces it with a link where user the user can first choose their Debian version. This change helps prevent typical users from borking their systems (see below).

Justification

The README.md's Debian install instructions link to winetricks within Debian's sid (unstable) package list. This is fine if someone downloads the winetricks .deb and installs manually, but at the download page the Debian site actually advises against this:

If you are running Debian, it is strongly suggested to use a package manager like aptitude or synaptic to download and install packages, instead of doing so manually via this website.

You should be able to use any of the listed mirrors by adding a line to your /etc/apt/sources.list like this:

deb http://ftp.de.debian.org/debian sid main contrib

Following those instructions is a very bad idea for most users as it creates a difficult-to-unwind "FrankenDebian" situation for those running stable Debian (which is most users). It's not clear to those who might land on that page from the winetricks README.md link that the instructions pertain only to unstable Debian. The change in this PR sends the user to a page where they must choose their appropriate version of Debian.

[austin987]

Change seems fine, but that link is giving me a 503 (and regular search returns no results). I'll try again later.