contrib: install PyOxidizer in Linux and Windows environments
For Linux, this was trivial.
For Windows, we need to teach the powershell script to install
Rust as well. This was also pretty straightforward.
Differential Revision: https://phab.mercurial-scm.org/D8468
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install::
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing::
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See https://mercurial-scm.org/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.