include describing the new release in RELEASING.md

RELEASING.md

@@ -17,6 +17,7 @@ https://github.com/Codearte/gradle-nexus-staging-plugin#server-credentials.
  1. When the build has successfully completed, run `./gradlew closeAndReleaseRepo`. If this times out
     or fails some other way, log in manually to https://oss.sonatype.org/ and either complete the
     release through closing and releasing the staging repository, or by cleaning up and rerunning.
+ 1. Add a description of the new release at https://github.com/spotify/mobius/releases.
  1. Once the new set of artifacts is available on https://repo.maven.apache.org/maven2/com/spotify/mobius/, update the
     `baselineVersion` property in [binary_compatibility.gradle](gradle/binary_compatibility.gradle) to the
     version that was just released.