Added linux build instructions to README

* Added install instructions for linux
* Added text for the Getting OpenSurgSim section
* Moved dependencies to the end, as an appendix (I think this is better)
Fixed some spelling and spacing in README
README: Clean up compiler requirement in windows section
Pick boost 1.55 for install instruction in README

The meta package libboost-all-dev is messed up on Ubuntu 14.04, it
doesn't install. However, the 1.55 version works fine for some reason.