Change the template in release-drafter.yml (#1050)

Author: nakamura-to

.github/release-drafter.yml

@@ -1,8 +1,12 @@
 name-template: '$RESOLVED_VERSION'
 tag-template: '$RESOLVED_VERSION'
 template: |
+  # What's Changed
 
   $CHANGES
+  
+  **Full Changelog**: https://github.com/$OWNER/$REPOSITORY/compare/$PREVIOUS_TAG...v$RESOLVED_VERSION
+
 categories:
   - title: 'New Features'
     labels: