doc: add link to contributing instructions to CONTRIBUTING.md
doc: add link to contributing instructions to CONTRIBUTING.md

jonmbake/checkstyle,sharang108/checkstyle,liscju/checkstyle,checkstyle/checkstyle,romani/checkstyle,checkstyle/checkstyle,ilanKeshet/checkstyle,jonmbake/checkstyle,jonmbake/checkstyle,sharang108/checkstyle,sabaka/checkstyle,romani/checkstyle,checkstyle/checkstyle,ilanKeshet/checkstyle,rnveach/checkstyle,liscju/checkstyle,jochenvdv/checkstyle,sabaka/checkstyle,romani/checkstyle,romani/checkstyle,rnveach/checkstyle,romani/checkstyle,checkstyle/checkstyle,ilanKeshet/checkstyle,checkstyle/checkstyle,jochenvdv/checkstyle,rnveach/checkstyle,liscju/checkstyle,rnveach/checkstyle,rnveach/checkstyle,jochenvdv/checkstyle,romani/checkstyle,sharang108/checkstyle,checkstyle/checkstyle,rnveach/checkstyle,sabaka/checkstyle