docs: add FAQ on increasing concurrency limit (#281)

Author: beran-t

docs.json

@@ -250,6 +250,7 @@
           {
             "group": "FAQ",
             "pages": [
+              "docs/faq/increase-concurrency",
               "docs/faq/paused-sandboxes-concurrency",
               "docs/faq/template-limit",
               "docs/faq/public-templates",

docs/faq/increase-concurrency.mdx

@@ -0,0 +1,30 @@
+---
+title: "How do I increase my concurrency limit?"
+sidebarTitle: Increasing concurrency
+---
+
+You can raise your number of [concurrent sandboxes](/docs/billing#plans) by purchasing self-serve concurrency add-ons from the [dashboard billing tab](https://e2b.dev/dashboard?tab=billing). 
+
+For higher limits at lower prices, commit to a minimum monthly usage for a year on the [Enterprise plan](/docs/billing#plans) by [contacting sales](mailto:enterprise@e2b.dev).
+
+<AccordionGroup>
+  <Accordion title="How much concurrency does each add-on add, and what's the self-serve maximum?">
+    Each add-on adds 500 concurrent sandbox slots. On the Pro tier, you can scale this way up to 1,100 concurrent sandboxes. To go higher, you need an Enterprise plan.
+  </Accordion>
+
+  <Accordion title="What's the per-unit pricing?">
+    $500/month per add-on (500 slots), charged on top of your usage bill.
+  </Accordion>
+
+  <Accordion title="Does the increase take effect immediately?">
+    Yes. The higher limit applies as soon as you purchase the add-on, with no provisioning delay.
+  </Accordion>
+
+  <Accordion title="Can I scale the add-ons back down later?">
+    Yes. Add-ons are billed monthly and are non-refundable, but you can remove one to stop future charges, so you are not locked in beyond the current billing period.
+  </Accordion>
+
+  <Accordion title="How is a mid-cycle purchase billed?">
+    The dashboard shows the exact amount you will be charged before you confirm the purchase.
+  </Accordion>
+</AccordionGroup>