DOC: Edit MultiIndex.set_levels() docstring to clarify that set_levels() interprets passed values as new components of the .levels attribute (#28294)
Added documentation on MultiIndex.set_levels to clarify that MultiIndex.set_levels() interprets passed values as new components of the .levels attribute. Continuation of #28797 due to issues with Travis CI for Python 3.8 and subsequent git diff issues resulting from resolution of Travis CI issues.

- [x] closes #28294 - or at least attempts to
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
can you rebase Hello @jbrockmendel, do you mean 'git rebase upstream/master' or 'git fetch upstream && git merge upstream/master' to resolve conflicts?

Just wanted to confirm in order to avoid the git diff issues I encountered earlier in #28797  > do you mean 'git rebase upstream/master' or 'git fetch upstream && git merge upstream/master' to resolve conflicts?

I usually do `git pull upstream master` and manually resolve any conflicts. Not sure what happened, but I did a `git fetch upstream`, `git pull upstream/master`, manually resolved conflicts, and `git push origin` on my branch - and my tests are failing.

Edit: Did a `git fetch upstream && git merge upstream/master`, checked `black pandas` and `git diff`, and `git push origin` on my branch to get latest updates - tests passed. lgtm @gfyoung care to take a look? Hello @hweecat! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:



There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-01-02 01:51:02 UTC can you merge master @jbrockmendel I've done a "git fetch upstream" and "git merge upstream/master" - let's hope tests pass this time. Okay, I have no idea what happened to my branch when I'm merging master, and tests are failing - suspect that it's caused by my previous commits made by merging master.

Anyone has any idea what to do with this? Did you merge `upstream/master` or master from your branch? I'm guessing the latter given the amount of files changed

You can maybe reset hard back to before the merge and try again with `upstream/master` Just checked - tests finally passed after the reset hard and merge with `upstream master`. Thanks for the help! Thanks for the work on this @hweecat 