Set version and release date in ChangeLog

Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>
diff --git a/ChangeLog b/ChangeLog
index e7f16a9..47e2b5a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,6 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
-= mbed TLS x.x.x branch released xxxx-xx-xx
+= mbed TLS 2.16.11 branch released 2021-07-07
 
 Security
    * Fix a bias in the generation of finite-field Diffie-Hellman-Merkle (DHM)