Fix these links, as they appear to be broken (#1595)

Fix these links, as they appear to be broken (#1595)

It looks like build_environment_setup.md got renamed to
getting_started_build_tools.md in this commit:

	commit e6c638bed1fa0a48bb6f8697b2a61717c4fd0992
	Author: skullY <skullydazed@gmail.com>
	Date:   Sat Aug 5 20:54:34 2017 -0700

		Overhaul the Getting Started section and add a FAQ section

	 docs/{build_environment_setup.md => getting_started_build_tools.md} | 132 ++++++++++++++++++++++++++++++++++++-------------------------------------

This commit adjusts the links to match the new name.