Fixed the memory usage explanation of categorical in gotchas from O(n…#17736

Merged

jreback merged 1 commit intopandas-dev:masterfrom

berkay-dincer:master

Oct 2, 2017

Commits on Oct 2, 2017

Fixed the memory usage explanation of categorical in gotchas from O(nm) to O(n+m)
trberkad
committed