Update: 	* Add a .gitignore file

Summary: Signed-off-by: Gnanakeethan Balasubramaniam <gnanakeethan@gmail.com>

Test Plan: no plans yet

Reviewers: sanjoydesk

Reviewed By: sanjoydesk

Subscribers: gnanakeethan, sanjoydesk

Differential Revision: http://phabricator.gnanakeethan.tk/D2