README: Mention where to find changelogs

Refs twbs#16739
[skip sauce]

Author: cvrebert

README.md

@@ -118,6 +118,8 @@ Get updates on Bootstrap's development and chat with the project maintainers and
 
 For transparency into our release cycle and in striving to maintain backward compatibility, Bootstrap is maintained under [the Semantic Versioning guidelines](http://semver.org/). Sometimes we screw up, but we'll adhere to those rules whenever possible.
 
+See [the Releases section of our GitHub project](https://github.com/twbs/bootstrap/releases) for changelogs for each release version of Bootstrap. Release announcement posts on [the official Bootstrap blog](http://blog.getbootstrap.com) contain summaries of the most noteworthy changes made in each release.
+
 
 
 ## Creators