Add a sentence in CHANGES to note SM2 support

Reviewed-by: NTim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7160)

CHANGES

@@ -9,6 +9,9 @@
 
  Changes between 1.1.0i and 1.1.1 [xx XXX xxxx]
 
+  *) Add SM2 base algorithm support.
+     [Jack Lloyd]
+
   *) s390x assembly pack: add (improved) hardware-support for the following
      cryptographic primitives: sha3, shake, aes-gcm, aes-ccm, aes-ctr, aes-ofb,
      aes-cfb/cfb8, aes-ecb.