DOC: mention other packages in IO docs (for now, just xray for netCDF)
As discussed in #5487.

This would also be a nice place to mention other packages that connect the
pandas DataFrames with other file formats. Right now, the only one I can think
of off-hand is `root_pandas` (#9378, CC @ibab), but I'm sure there are more.

@cpcloud should add `odo` here
 Looks good to me! 
Maybe adding a small snippet of a typical code example how you read in a file and convert to dataframe? (just a code-block, not executing it)
 Could add `impyla`
 thanks @shoyer 
 Thanks for the suggestions, guys. I'm going to do a followup adding a small example for netCDF/xray, but I'll leave odo and impyla examples to others who are more familiar with those tools.
