Update link in discounts page (#13669)

Right now, `/discounts` is the top search result for 'posthog discounts'. 

While it's fun, for people actually looking for our discounts, we should then easily link them to our discounts page in the handbook, rather than the pricing page, which talks about a much more niche set of discounts, and only if you hover over the right place.

Author: charlescook-ph

src/pages/discounts/index.tsx

@@ -192,8 +192,8 @@ export default function Discounts(): JSX.Element {
                 <p>
                     We price our products fairly and offer discounts based on usage and deal terms – you can read all
                     about them{' '}
-                    <Link to="/pricing#discounts" state={{ newWindow: true }}>
-                        on our pricing page.
+                    <Link to="/handbook/growth/sales/contract-rules#discounts" state={{ newWindow: true }}>
+                        in our handbook.
                     </Link>
                 </p>
                 <p>But sometimes this leaves our customers feeling left out. They want huge discounts too!</p>