Updated Release schedule (markdown)

Release-schedule.md

@@ -1,5 +1,7 @@
 New feature releases of Wagtail are released every three months. These releases provide new features, improvements and bugfixes, and are marked by incrementing the second part of the version number (for example, 2.6 to 2.7).
 
+View the [Wagtail roadmap](https://wagtail.org/roadmap/) to learn about upcoming improvements.
+
 ## Future and current versions
 
 Here are planned future releases and currently-supported Wagtail versions.