Update CONTRIBUTING.md
Update CONTRIBUTING.md

removed the links to INSTALL from ToC
openSNP/snpr,philippbayer/snpr,vivekiitkgp/snpr,openSNP/snpr,vivekiitkgp/snpr,vivekiitkgp/snpr,gedankenstuecke/snpr,philippbayer/snpr,philippbayer/snpr,vivekiitkgp/snpr,philippbayer/snpr,gedankenstuecke/snpr,gedankenstuecke/snpr,gedankenstuecke/snpr,openSNP/snpr,openSNP/snpr