docs: Clarify branch compatibility

Author: adi-ray

src/content/contributor-docs/en/contributing_to_the_p5js_reference.mdx

@@ -380,7 +380,12 @@ Class constructors are defined with the `@class` tag and the `@constructor` tag.
 
 The p5.js repository is set up so that you can generate and preview the reference without needing to build and run the p5.js website as well.
 
-To do so, make sure you have committed your changes to a branch of your fork of p5.js.
+To do so, make sure you have committed and pushed your changes to a branch of your fork of p5.js.
+
+**Important:** Make sure you're working with compatible branches:
+
+- Use the `2.0` branch of p5.js-website with the `dev-2.0` branch of p5.js
+- Use the `main` branch of p5.js-website with the `main` branch of p5.js
 
 * First, ensure you have the necessary dependencies installed in the p5.js-website repository: