04/02: mention local traces

Author: kettanaito

exercises/04.debugging/02.solution.trace-viewer/README.mdx

@@ -4,6 +4,16 @@ Good job! 👏
 
 Please wait for the others to finish so we could go through the solution to this exercise together.
 
+## Generating local traces
+
+You can generate a trace of your local test run by setting the `--trace` CLI option of `playwright` to `on`:
+
+```sh
+npx playwright test --trace on
+# or
+npm run test:e2e -- --trace on
+```
+
 ## Related materials
 
 - [Trace Viewer](https://playwright.dev/docs/trace-viewer)