MAINTAINERS: add instrumentation documentation path

Add path to Instrumentation documentation to the corresponding area.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

Author: kartben

MAINTAINERS.yml

@@ -2920,6 +2920,7 @@ Instrumentation Subsystem:
     - fkokosinski
     - tgorochowik
   files:
+    - doc/services/instrumentation/
     - include/zephyr/instrumentation/
     - samples/subsys/instrumentation/
     - scripts/instrumentation/