Update ChangeLog

Update ChangeLog with a less ambigous description.
diff --git a/ChangeLog b/ChangeLog
index ea5740c..b80af6e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -10,8 +10,8 @@
    * Clarify documentation for mbedtls_ssl_write() to include 0 as a valid
      return value. Found by @davidwu2000. #839
    * Add ecc extensions only if an ecc based ciphersuite is used.
-     Affects interoperability with BouncyCastle and other peers.
-     Raised by milenamil in #1157.
+     This improves compliance to RFC 4492, and as a result, solves
+     interoperability issues with BouncyCastle. Raised by milenamil in #1157.
 
 = mbed TLS 2.7.4 branch released 2018-06-18