add install script for installing mvfst
add install script for installing mvfst

Reviewed By: mjoras

Differential Revision: D19914554

fbshipit-source-id: e1ee1c26849378cb6b27a4d4a889e86b5e1f06ad

facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst