Update users_sf2gh.json
Update users_sf2gh.json

Added SF2gh mapping for myself.  -David
geneontology/go-site,mugitty/go-site,cooperl09/go-site,ValWood/go-site,mugitty/go-site,hattrill/go-site,hattrill/go-site,hattrill/go-site,ValWood/go-site,geneontology/go-site,cooperl09/go-site,mugitty/go-site,cooperl09/go-site,ValWood/go-site,mugitty/go-site,geneontology/go-site,hattrill/go-site,geneontology/go-site,geneontology/go-site,hattrill/go-site,ValWood/go-site,cooperl09/go-site