Update early-adopter.mdx (#6122)

* Update early-adopter.mdx

Add File IO to list of EA features

* Update src/docs/product/accounts/early-adopter.mdx

Author: lizokm

src/docs/product/accounts/early-adopter.mdx

@@ -20,4 +20,5 @@ Limitations:
 - [Grouping Breakdown](/product/data-management-settings/event-grouping/grouping-breakdown/)
 - [Issue Reprocessing](/product/issues/reprocessing/)
 - [Span Summary](/product/performance/transaction-summary/#span-summary)
+- [File IO on Main Thread for Mobile](/product/issues/issue-details/performance-issues/main-thread-io/)
 - Organization Domains - Instead of being a path segment, organization slugs are used as a subdomain for [sentry.io](https://sentry.io). For example, `https://acme.sentry.io/issues/` replaces `https://sentry.io/organizations/acme/issues/`. API URLs are unchanged.