* Update intro.rst to mention Python 3.6
The homepage mentions 3.6, so I update this section to be in line
* Create upgrade-python-version.rst
Add news item for https://github.com/xonsh/xonsh/pull/5193
"try xonsh" link is non-functional and is likely disappointing to new users who
try to use it.
quick other doc-related fix to re-install xonsh before second `doctr deploy` to
make sure that documentation that is uploaded reflects the last tagged release.