CHANGES: mention blinding reverting in ECDSA. [skip ci]

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: David Benjamin <davidben@google.com>
(Merged from #6664)

CHANGES

@@ -9,6 +9,10 @@
 
  Changes between 1.1.0h and 1.1.1 [xx XXX xxxx]
 
+  *) Revert blinding in ECDSA sign and instead make problematic addition
+     length-invariant. Switch even to fixed-length Montgomery multiplication.
+     [Andy Polyakov]
+
   *) Use the new ec_scalar_mul_ladder scaffold to implement a specialized ladder
      step for binary curves. The new implementation is based on formulas from
      differential addition-and-doubling in mixed Lopez-Dahab projective