A remark on projective embeddings of varieties with non-negative cotangent bundles. On moduli of stable 2-bundles with small Chern classes on \(Q_ 3\). Appendix by Nicolae Manolache: The curves \(Y\) of degree 6 with \(\omega_ Y= {\mathcal O}_ Y(-1)\) on a smooth quadric \(Q_ 3\) 