chore(nextjs): Add compatibility note to README (#4110)

There are a number of changes in Next 12 which have the potential to break folks using our SDK. Until we make changes to fix that, this clarifies what users can expect to work and not.

Author: lobsterkatie

packages/nextjs/README.md

@@ -17,6 +17,10 @@
 - [Official SDK Docs](https://docs.sentry.io/platforms/javascript/guides/nextjs/)
 - [TypeDoc](http://getsentry.github.io/sentry-javascript/)
 
+## Compatibility
+
+Currently, the Sentry Next.js SDK supports Next.js versions `10.0.8` - `11.1.3`. The SDK may work with some projects using Next.js 12, but it is not yet officially supported.
+
 ## General
 
 This package is a wrapper around `@sentry/node` for the server and `@sentry/react` for the client, with added functionality related to Next.js.