update README
update README

the documentation link was dead, and newer version are only accessible
with a community.aldebaran.com account.

Change-Id: I7b9c6ab4ab1930d1f2cd1ff4a4d1ce3049b35f5f

aldebaran/libalmath,sbarthelemy/libalmath,sbarthelemy/libalmath,aldebaran/libalmath