Add support contact note for higher CPU/RAM limits

Users can now see they should contact support@e2b.dev if they need
higher CPU or RAM limits than the defaults.

Author: beran-t

docs/billing.mdx

@@ -18,7 +18,7 @@ E2B uses [usage-based pricing](#usage-based-pricing) - you pay only for what you
 | **Concurrent sandboxes** | 20 | 100 - 1,100 | 1,100+ |
 
 <Note>
-Pro plan includes 100 concurrent sandboxes. Higher concurrency up to 1,100 is available as a purchasable [add-on](https://e2b.dev/dashboard/tberan/billing).
+Pro plan includes 100 concurrent sandboxes. Higher concurrency up to 1,100 is available as a purchasable [add-on](https://e2b.dev/dashboard/tberan/billing). Need higher CPU or RAM limits? Contact [support@e2b.dev](mailto:support@e2b.dev) for more information.
 </Note>
 
 Plans have different [API rate limits](/docs/sandbox/rate-limits).