Update BUILD instructions

[teward]

Maintainer of primary repo has said to use "Master" instead of the Stable branch because of dltray, etc. problems. Further, sudo make install can in fact harm your system, but if you are on any mainstream distribution, checkinstall is actually available in most repositories and builds a native-package-manager-compatibile package around what sudo make install does and then installs that package so you can easily revert afterwards. This tends to be the safer option.

[TheAssassin]

Thank you for your contribution. I left some comments.