minor #13723 Update reactjs.rst (abdounikarim)

This PR was submitted for the 5.0 branch but it was merged into the 3.4 branch instead.

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Update reactjs.rst

update content

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4ef42f1 Update reactjs.rst

Author: javiereguiluz

frontend/encore/reactjs.rst

@@ -6,7 +6,14 @@ Enabling React.js
 
     Do you prefer video tutorials? Check out the `React.js screencast series`_.
 
-Using React? First enable support for it in ``webpack.config.js``:
+Using React? First add some dependencies with Yarn:
+
+.. code-block:: terminal
+
+    $ yarn add @babel/preset-react --dev
+    $ yarn add react react-dom prop-types
+
+Enable react in your ``webpack.config.js``:
 
 .. code-block:: diff