xz-utils/README.Debian: Document patches

Given that we are packaging an alpha release, end-users and other
distributors might wonder how a stable release is made out of that and
what the differences from the original code are.

Add a note to README.Debian describing each patch to help them,
imitating the gcc packaging.  This information goes here and not in
the package description because it is more relevant when using the
package than when deciding whether to install it.  The package
description already mentions that threads are not supported.

Thanks to Andrew Pollock, Thorsten Glaser, and Lasse Collin for
advice.
2 files changed