Update contributing docs to reference main branch (#12815)
Update contributing docs to reference main branch (#12815)

no issue
ErisDS/Ghost,e10/Ghost,TryGhost/Ghost,janvt/Ghost,ErisDS/Ghost,e10/Ghost,TryGhost/Ghost,bitjson/Ghost,janvt/Ghost,ErisDS/Ghost,TryGhost/Ghost,bitjson/Ghost