doc: clarify usage of coverage reporters

PR-URL: https://github.com/nodejs/node/pull/53523
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Chemi Atlow <chemi@atlow.co.il>

doc/api/test.md

@@ -508,6 +508,9 @@ used as an in depth coverage report.
 node --test --experimental-test-coverage --test-reporter=lcov --test-reporter-destination=lcov.info
 ```
 
+* No test results are reported by this reporter.
+* This reporter should ideally be used alongside another reporter.
+
 ### Limitations
 
 The test runner's code coverage functionality does not support excluding