[Chapel Merge] Update prereqs.rst for python 3

Branch: refs/heads/master
Revision: 0097f3d
Author: mppf
Log Message:

Merge pull request #16618 from mppf/update-prereqs-python-3

Update prereqs.rst for python 3

Follow-up to PR #16560

  • Update prereqs.rst to describe Python 3 requirements
  • While there, I noticed a make that should be $(MAKE) in
    doc/Makefile, so fix that too

I tested the updated suggested package-install commands (see PR #16619).
I removed the OpenSUSE section because I was unable to test with a recent

Reviewed by @lydia-duncan - thanks!

Modified Files:
M doc/Makefile
M doc/rst/usingchapel/prereqs.rst

Compare: https://github.com/chapel-lang/chapel/compare/d6e5d0ab33e8...0097f3d377f0