MAINT: update docs/release.rst to remind version branch merge
MAINT: update docs/release.rst to remind version branch merge

scikit-umfpack/scikit-umfpack,scikit-umfpack/scikit-umfpack,rc/scikit-umfpack-rc,rc/scikit-umfpack,rc/scikit-umfpack,rc/scikit-umfpack-rc