docs: update perf disclaimer

docs/intro/what_is_envoy.rst

@@ -111,9 +111,8 @@ the :ref:`administration <operations_admin_interface>` port. Envoy also supports
 Design goals
 ^^^^^^^^^^^^
 
-A short note on the design goals of the code itself: Although Envoy is by no means slow,
-little effort has been put into micro performance optimizations of the native code. Fans of deep
-performance tuning will find ample opportunity for improvement. The code has been written to be
-modular and easy to test versus aiming for the greatest possible absolute performance. It's our
-view that this is a more efficient use of time given that typical deployments will be alongside
-languages and runtimes many times slower and with many times greater memory usage.
+A short note on the design goals of the code itself: Although Envoy is by no means slow (we have
+spent considerable time optimizing certain fast paths), the code has been written to be modular and
+easy to test versus aiming for the greatest possible absolute performance. It's our view that this
+is a more efficient use of time given that typical deployments will be alongside languages and
+runtimes many times slower and with many times greater memory usage.