Add more explanation about checking out the code from the git repository.
Add more explanation about checking out the code from the git repository.

caymard/openMVG,poparteu/openMVG,danylaksono/openMVG,yoshidaken/openMVG,poparteu/openMVG,Smozeley/openMVG,openMVG/openMVG,openMVG/openMVG,danylaksono/openMVG,yoshidaken/openMVG,caymard/openMVG,Smozeley/openMVG,Vinzza/openMVG,openMVG/openMVG,yoshidaken/openMVG,mojovski/openMVG,caymard/openMVG,poparteu/openMVG,openMVG/openMVG,openMVG/openMVG,poparteu/openMVG,Smozeley/openMVG,mojovski/openMVG,Vinzza/openMVG,danylaksono/openMVG,Vinzza/openMVG,mojovski/openMVG