doc: add clearer setup description

Updated console example to follow style of rest of the examples

PR-URL: https://github.com/nodejs/node/pull/15962
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

BUILDING.md

@@ -129,6 +129,9 @@ To run the tests:
 $ make test
 ```
 
+At this point you are ready to make code changes and re-run the tests!
+Optionally, continue below.
+
 To run the tests and generate code coverage reports:
 
 ```console
@@ -145,7 +148,7 @@ and overwrites the `lib/` directory. To clean up after generating the coverage
 reports:
 
 ```console
-make coverage-clean
+$ make coverage-clean
 ```
 
 To build the documentation: