feat(apple): Add comment about min on-prem version (#2915)

Add a comment about Sentry on-prem minimum version since sentry-cocoa 6.0.0.

Co-authored-by: Fiona <[email protected]>

Author: philipphofmann

src/platforms/apple/common/usage.mdx

@@ -52,6 +52,7 @@ This integration will swizzle some methods to create breadcrumbs e.g.: for `UIAp
 
 ## Known Limitations
 
+- Since version 6.0.0 of this SDK, Sentry on-premises version greater than version 20.6.0 is required. If you are using sentry.io, no action is needed.
 - We recommend upgrading to 6.x.x to get reliable <PlatformLink to="/configuration/releases/">Release Health</PlatformLink> data,
 as we added many improvements over 5.x.x, in which we introduced Release Health.
 - If you're currently using a version between 6.0.2 and 6.0.8, we **highly recommend** you upgrade to the latest version to avoid [a regression](https://github.com/getsentry/sentry-cocoa/pull/786) that affected the quality of the stacktraces and error messages, which was fixed in 6.0.9.