Update README

Author: EndBug

README.md

@@ -4,11 +4,14 @@ Action that generates website docs for branches and tags using docgen
 
 ## Usage
 
+**Imporant:** this action requires the `docs/docs.json` file to be built **before** the action is run.
+
 How to use it in a workflow:
 
 ```yaml
-- name: Build and deploy documentation
-  uses: dbots-pkg/action-docs@v1
+- run: npm run docs
+
+- uses: dbots-pkg/action-docs@v1
   env:
     GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 ```