Update CONTRIBUTING.md

CONTRIBUTING.md

@@ -71,6 +71,7 @@ Documentation is necessary for all non bugfix/refactoring changes.
 
 Only make changes to files that are in [`/packages/mermaid/src/docs`](packages/mermaid/src/docs)
 
-**_DO NOT CHANGE FILES IN `/docs`_**
+**_DO NOT CHANGE FILES IN `/docs` MANUALLY_**
+The `/docs` folder will be rebuilt and committed as part of a pre-commit hook.
 
 [Join our slack community if you want closer contact!](https://join.slack.com/t/mermaid-talk/shared_invite/enQtNzc4NDIyNzk4OTAyLWVhYjQxOTI2OTg4YmE1ZmJkY2Y4MTU3ODliYmIwOTY3NDJlYjA0YjIyZTdkMDMyZTUwOGI0NjEzYmEwODcwOTE)