README.md: Homebrew formula for OS X is available
manuals/ponysay.texinfo: installation on Mac OS X
Merge pull request #179 from jstepien/mac-os-x

README.md: Homebrew formula for OS X is available; and update to ponysay.texinfo too

Signer of: jsteplen
Signed of: Pablo Lezaeta <prflr88@gmail.com>