Fix README usage
Fix README usage

This code is not in pypi as giftwrap. Therefore, we cannot install it
as described in pip command. Until this code is in pypi, provide
alternate instructions.

blueboxgroup/giftwrap,blueboxjesse/giftwrap,blueboxjesse/giftwrap,blueboxgroup/giftwrap,j2sol/giftwrap,j2sol/giftwrap