Revert "Add bower installation step"

This reverts commit 05a664f8207f2aa7ec0d0901290274b0f13fbd71.

According to yeoman.io "bower" should be installed automatically
when installing "yo". It didn't work for me but that might be
due to a too old npm version installed (1.1.61) -- will file a
ticket next time rather than mess with the README...