Update CONTRIBUTING.md

CONTRIBUTING.md

@@ -199,7 +199,8 @@ Publishing is handled by a 2-branch [pre-release process](https://intuit.github.
 - PRs made into the default branch are auto-deployed to the `next` pre-release tag on NPM. The result can be installed with `npm install vega-lite/@next`.
   - When merging into `next`, please use the `squash and merge` strategy.
 - To release a new stable version, open a PR from `next` into `stable` using this [compare link](https://github.com/vega/vega-lite/compare/stable...next).
-  - When merging from `next` into `stable`, please use the `create a merge commit` strategy.
+  - When merging from `next` into `stable`, please use the `create a merge commit` strategy. 
+  - After the release note is generated (from commits), please take a look to clean up so the log is readable to the community.
 
 ## Suggested Programming Environment.