Update README.markdown
Update README.markdown

ClusterLabs not clusterlabs - git hub is case sensitive now days.
ClusterLabs/libqb,ClusterLabs/libqb,kgaillot/libqb,kgaillot/libqb,rubenk/libqb,ClusterLabs/libqb,davidvossel/libqb,davidvossel/libqb,kgaillot/libqb,gao-yan/libqb,rubenk/libqb,gao-yan/libqb