docs: Add a backlink to bytes.dev (#3429)

* docs: updates for new react-query course

Change removes convert kit for email capture and migrates it to Bytes. Copy updates to promote the new React Query Course are included.

* Add the PPP discount banner for the ui.dev React Query course.

* Add a backlink to Bytes.

Co-authored-by: Benjamin Adam <[email protected]>

Author: alexanderson1993

docs/src/components/Footer.js

@@ -96,8 +96,11 @@ export const Footer = props => {
               Subscribe to Bytes
             </h4>
             <p className="mt-4 text-gray-500 text-base leading-6 mb-4">
-              The best JavaScript newsletter! Delivered every Monday to over
-              76,000 devs.
+              The{' '}
+              <a href="https://bytes.dev/?r=tanstack">
+                best JavaScript newsletter!
+              </a>{' '}
+              Delivered every Monday to over 76,000 devs.
             </p>
             <BytesForm />
           </div>