add notes on process cpu usage

Author: copperlight

docs/spectator/lang/py/usage.md

@@ -381,3 +381,6 @@ observed the following single-threaded performance numbers across a two-minute t
 The benchmark incremented a single counter with two tags in a tight loop, to simulate real-world tag
 usage, and the rate-per-second observed on the corresponding Atlas graph matched. The protocol line
 was `74` characters in length.
+
+The Python process CPU usage was ~100% and the `spectatord` process CPU usage was ~55% on this 8 vCPU
+system.