DOC: Add MultiIndex.get_locs to generated reference
This should fix the failing CI, see https://github.com/pandas-dev/pandas/pull/30226

CLoses #30235 
@jorisvandenbossche I pushed some formatting changes to get this passing. Just the 32-bit failure being handled elsewhere. Will merge when travis passes. Things should be good on master once this is merged, thanks to #30237. Thanks for the fixup!