docs: attribute the Pinokio stutter report accurately

The workaround came from one Pinokio 8.2.0 user who did not state an OS, and a
single report suggests rather than isolates the embedded-browser cause.

docs/PERFORMANCE.md

@@ -129,11 +129,11 @@ Use the same controls before attributing a difference to the application:
 7. Treat a live-source outage as missing coverage, not as evidence of low client
    rendering cost.
 8. Record whether the app is running in Pinokio's embedded view or in an
-   external browser. The same Pinokio 8.2.0 Linux server was reported as
-   severely stuttery in the embedded view and smooth when its local URL was
-   opened directly in a normal browser ([#365](https://github.com/bilawalsidhu/gods-eye-view/issues/365)).
-   Treat that as a browser/compositor-path difference until the GPU renderer
-   proves otherwise.
+   external browser. One Pinokio 8.2.0 user reported severe stutter in the
+   embedded view that went away when the same local URL was opened in a normal
+   browser ([#365](https://github.com/bilawalsidhu/gods-eye-view/issues/365)).
+   Do not compare embedded-view and external-browser measurements directly;
+   compare the reported GPU renderer and matched scene settings first.
 
 ## What is not established yet