Mention FormatFile's in_place argument in readme.
Mention FormatFile's in_place argument in readme.

Also fix a typo from updating the README in #157.

Note: in_place argument introduced in #158.

wklken/yapf,hayd/yapf,elviswf/yapf,bygloam/yapf,abduld/yapf,sbc100/yapf,google/yapf,thurday/yapf,nikolamilosevic86/yapf,sbc100/yapf,ambv/yapf,google/yapf,jamesblunt/yapf,lucius-feng/yapf,dmoliveira/yapf