[DOC] Mention FPS in log_diagnostics example (#2150)

Closes #2076

examples/README.md

@@ -142,7 +142,7 @@ Example | File | Description
 Example | File | Description
 --- | --- | ---
 `custom_diagnostic` | [`diagnostics/custom_diagnostic.rs`](./diagnostics/custom_diagnostic.rs) | Shows how to create a custom diagnostic
-`log_diagnostics` | [`diagnostics/log_diagnostics.rs`](./diagnostics/log_diagnostics.rs) | Add a plugin that logs diagnostics to the console
+`log_diagnostics` | [`diagnostics/log_diagnostics.rs`](./diagnostics/log_diagnostics.rs) | Add a plugin that logs diagnostics, like frames per second (FPS), to the console
 
 ## ECS (Entity Component System)