Add BLS12-381 recommendation

pairing/bn256/README.md

@@ -13,9 +13,11 @@ Barreto-Naehrig curve as described in
 http://cryptojedi.org/papers/dclxvi-20100714.pdf. Its output is compatible with
 the implementation described in that paper.
 
+### Warning
 This package previously claimed to operate at a 128-bit security level. However,
 recent improvements in attacks mean that is no longer true. See
-https://moderncrypto.org/mail-archive/curves/2016/000740.html.
+https://moderncrypto.org/mail-archive/curves/2016/000740.html. 
+We strongly recommend using the `BLS12-381` curve that still provide ~128-bit security and is not vulnerable to these improved attacks.
 
 ### Benchmarks