Add disk space to billing plans table

Author: beran-t

docs/billing.mdx

@@ -16,6 +16,7 @@ E2B uses [usage-based pricing](#usage-based-pricing) - you pay only for what you
 | **Free credits** | $100 (one-time) | $100 (one-time) | Custom |
 | **Max session length** | 1 hour | 24 hours | Custom |
 | **Concurrent sandboxes** | 20 | 100 - 1,100 | 1,100+ |
+| **Disk space** | 10 GB | 20 GB | Custom |
 
 <Note>
 Pro plan includes 100 concurrent sandboxes. Higher concurrency up to 1,100 is available as a purchasable [add-on](https://e2b.dev/dashboard?tab=billing).