Add entry about bw file header statistics

CHANGELOG.md

@@ -21,6 +21,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 - Write bw file only when the percentage of measured relays is bigger than 60%
   (#28062)
+- Add option to remove link when the percentage of measured relays is less than
+  the 60% and instead include some statistics in the header (#28076)
 
 ## [0.8.0] - 2018-10-08