fix(Unity): Expanded on known limitations when targeting WebGL (#15485)

Author: bitsandfoxes

docs/platforms/unity/troubleshooting/known-limitations.mdx

@@ -113,3 +113,8 @@ When targeting WebGL, you have the option of setting the `PlayerSettings.WebGL.e
 - Setting it to `WebGLExceptionSupport.None` is not supported by the SDK.
 - For the SDK to be able provide stack traces, the support needs to be set to `WebGLExceptionSupport.FullWithStacktrace`.
 - The SDK is currently not able to provide line numbers due to the IL2CPP backend not being available.
+- **Native crash detection is not available on WebGL.** The SDK cannot determine if the browser or tab crashed, which affects session tracking:
+  - Sessions with captured exceptions are marked as `Unhandled`
+  - Sessions where the tab/browser closes without a clean shutdown are marked as `Abnormal`
+  - The Crash Free Session Rate will show 100% since native `Crashed` status is unavailable
+  - Monitor both `Unhandled` and `Abnormal` session rates to track stability issues