Update release notes with recent work merged

Author: bgandon

ci/release_notes.md

@@ -1,3 +1,6 @@
 ### Improvements
 
 - Document why Alpine image can't be used for building to Go code
+- Deprecate the specific `skip_download` resource property in favor of the standard `no_get` [Concourse feature][no_get] (submitted in #10, thanks @brakel!)
+
+[no_get]: https://concourse-ci.org/put-step.html#schema.put.no_get