User-emu documentation mentions inexistent "runtime" downloads

This bug has been copied automatically from: https://bugs.launchpad.net/qemu/+bug/1884982
Reported by 'Mingye Wang' on 2020-06-24 :

The official documentation for the user-space emulator[1] contains many
references to binary blobs no longer provided by  QEMU.org for download.
The parts mentioning them should be rephrased to avoid confusion and
instructions for building these components should be provided (maybe as a
reference to the LFS book with some scripts, or... cut a deal with some
super slim Linux distros). The specific parts are:

* qemu-XXX-i386-wine.tar.gz, a wine build under the prefix /wine.
* qemu-runtime-i386-XXX-.tar.gz, a glibc build.

  [1]: https://www.qemu.org/docs/master/user/main.html

In addition, the documentation contains many other instances of inexistent
"tar.gz" files, such as in "Network emulation". Most of these are
inherited from the days of texi documentation more than 10 years ago, and
they are so old that GitHub's blame have become unreliable. Someone really
should run `fgrep -r 'tar.gz' doc' on the QEMU source tree.

The issue was previously reported as [2], but nobody bother enough to
google the filename to find out where the confused user got the idea from.

  [2]: https://www.mail-archive.com/qemu-devel@nongnu.org/msg569174.html