add process to contentTracing doc

docs/api/content-tracing.md

@@ -3,6 +3,8 @@
 > Collect tracing data from Chromium's content module for finding performance
 bottlenecks and slow operations.
 
+Process: [Main](../tutorial/quick-start.md#main-process)
+
 This module does not include a web interface so you need to open
 `chrome://tracing/` in a Chrome browser and load the generated file to view the
 result.