docs: add v2 docs links

Author: babycourageous

README.md

@@ -28,6 +28,7 @@ Enjoy this library? Try the entire [TanStack](https://tanstack.com)! [React Tabl
 
 ## Visit [react-query.tanstack.com](https://react-query.tanstack.com) for docs, guides, API and more!
 
+Still on **React Query v2**? No problem! Check out the v2 docs here: https://react-query-v2.tanstack.com/.
 ## Quick Features
 
 - Transport/protocol/backend agnostic data fetching (REST, GraphQL, promises, whatever!)

docs/src/components/Nav.js

@@ -24,9 +24,18 @@ export const Nav = () => (
         <div className="flex flex-grow items-center justify-between w-3/4 md:w-auto md:justify-end space-x-4 md:space-x-8 h-16">
           <div className="flex space-x-4 md:space-x-8 text-sm md:text-base">
             <div>
+              Docs (
               <Link href="/overview">
-                <a className="leading-6 font-medium">Docs</a>
-              </Link>
+                <a className="leading-6 font-medium">v3</a>
+              </Link>{' '}
+              /{' '}
+              <a
+                href="https://react-query-v2.tanstack.com/docs/overview"
+                className="leading-6 font-medium"
+              >
+                v2
+              </a>
+              )
             </div>
             <div>
               <Link href="/examples/simple">