Add ChangeLog entry

Add a ChangeLog entry for Jonathan Bennett's contribution which allows
loading symlinked certificates.
diff --git a/ChangeLog b/ChangeLog
index 60018b55..5d77df2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -75,6 +75,8 @@
 
 Bugfix
    * Fix an unchecked call to mbedtls_md() in the x509write module.
+   * Allow loading symlinked certificates. Fixes #3005. Reported and fixed
+     by Jonathan Bennett <JBennett@incomsystems.biz> via #3008.
 
 = mbed TLS 2.16.4 branch released 2020-01-15