Updated release instructions to use rst instead of markdown
- [ ] closes #50824 
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).

@datapythonista I tried to fix the other pull request but made a mess of it so I thought it would be best to start over. If this was the wrong, please let me know what should have been done; still learning the GitHub/ git workflow.


Thanks @tpackard1 