Add an entry in NEWS about the new threading API

Reviewed-by: Richard Levitte <levitte@openssl.org>

NEWS

diff --git a/NEWS b/NEWS
index 240bd0a..c3538f5 100644
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,7 @@
 
   Major changes between OpenSSL 1.0.2g and OpenSSL 1.1.0 [in pre-release]
 
+      o New threading API implemented
       o Support for ChaCha20 and Poly1305 added to libcrypto and libssl
       o Support for extended master secret
       o CCM ciphersuites