DOC: Add example for multiindex series and dataframe merge
- [x] closes #12550


@simonjayhawkins  all green now  Pushed some changes and simplified the example  - seems CI failure is unrelated Rebased, all green now @WillAyd  All green  Thanks @ryankarlos @datapythonista can we see these merged changes or is #32279 preventing the publishing of the dev docs  > @datapythonista can we see these merged changes or is #32279 preventing the publishing of the dev docs

Development (master) website and docs should be available at pandas.io (dev.pandas.io should have the same, but it's the one being affected by that problem). cool. should the link to the contributing guide in README.md point to https://pandas.io/docs/development/contributing.html instead of https://dev.pandas.io/docs/contributing.html @ryankarlos looking at the rendered output at  https://pandas.io/docs/user_guide/merging.html, the result is not displayed. see https://github.com/pandas-dev/pandas/pull/32068#discussion_r383482432 @datapythonista from the pandas.io link, is there a link to the latest released docs (i.e. 1.0.1). the documentation link under Latest version: 1.0.1 links to 1.1.0.dev0+641.g7d9c20073 docs whereas the docs links to previous versions link to the correct docs. @simonjayhawkins I sent an email to pandas-dev some days ago to try decide on the domains. Originally everybody looked happy with just using directories under pandas.io. But looks like finally the preference is to drop pandas.io (including dev.pandas.io), and just use pandas.pydata.org (the dev docs should be a directory there). The first PR to move into that direction is giving some problems with the ssh key, and I don't have permissions to this repo settings and not yet to the server. So things will move slowly until we clean up the mess with the domains and the structure.  Thanks @datapythonista So it maybe worth updating the README.md, even as a temporary measure, as I think it is important this link should point to the latest docs. I'll open a PR for this.