A typo fix, and a missing doc string added
A typo fix, and a missing doc string added

vodik/plumbum,tomerfiliba/plumbum,weka-io/plumbum,vodik/plumbum,AndydeCleyre/plumbum,pombredanne/plumbum,fahhem/plumbum,henryiii/plumbum,pombredanne/plumbum,fahhem/plumbum,henryiii/plumbum,tomerfiliba/plumbum,AndydeCleyre/plumbum,weka-io/plumbum