Add cswitch stacks to xperf command line

Things are sort of broken without cswitch for now.

Author: jrmuizel

etw-gecko/README.md

@@ -19,7 +19,7 @@ To install `profiler-symbol-server`, run `cargo install profiler-symbol-server`.
 
 Open an Administrator command shell with Win+R, "cmd", Ctrl+Shift+Enter.
 
-Start profiling session by running `xperf -on latency -stackwalk profile` in the Adminstrator shell. Then run `xperf -d out.etl` to capture it.
+Start profiling session by running `xperf -on latency -stackwalk profile+cswitch` in the Adminstrator shell. Then run `xperf -d out.etl` to capture it.
 
 Then run `cargo run --release out.etl [process-name]` to produce a gecko.json.