Include build instructions, including pre-requisites.

I couldn't remember the build pre-requisites so I put them here
Don't track any of the binary files left over from compiling
Clean up any left over agsgame.log files with a 'make clean'
Revert "Clean up any left over agsgame.log files with a 'make clean'"

This reverts commit c54d5192f71bffd8d1ed9bb66024366b2930f294.
Change filenames to BUILD_QUICK and add links to full instructions