Added README.md file for ForkLift plugin

plugins/forklift/README.md

+## forklift
+
+Plugin for ForkLift, an FTP application for OS X.
+
+### Requirements
+
+* [ForkLift](http://forkliftapp.com/forklift/)
+
+### Usage
+
+* If `fl` is called without arguments then the current folder is opened in ForkLift. Is equivalent to `fl .`
+
+* If `fl` is called with a directory as the argument, then that directory is opened in ForkLift
\ No newline at end of file