A lot of people seem to point out this line as a gotcha when certain
features haven't been released yet. It's been more of a pain-point
than a marketing win since people seem to be unaware of the way this
project is developed.
Fix#7401
### Summary
"In 2016, with the release of macOS 10.12 Sierra, the name was changed from OS X to macOS"
source :: https://en.wikipedia.org/wiki/MacOS#macOS
### Checklist
- [ ] If code changes were made then they have been tested.
- [ ] I have updated the documentation to reflect the changes.
- [ ] This PR fixes an issue.
- [ ] This PR adds something new (e.g. new method or parameters).
- [ ] This PR is a breaking change (e.g. methods or parameters removed/renamed)
- [X] This PR is **not** a code change (e.g. documentation, README, ...)
Add long_description_content_type in setup.py, fix incorrectly
matched up title underlines in README.rst, and fix incorrect entry in
MANIFEST.in that was forgotten when the README was renamed in 06296bf.
