doc: add clearer setup description · nodejs/node@5472173

Original file line number	Diff line number	Diff line change
`@@ -129,6 +129,9 @@ To run the tests:`
`129`	`129`	`$ make test`
`130`	`130`	```
`131`	`131`
	`132`	`+At this point you are ready to make code changes and re-run the tests!`
	`133`	`+Optionally, continue below.`
	`134`	`+`
`132`	`135`	`To run the tests and generate code coverage reports:`
`133`	`136`
`134`	`137`	```console
@@ -145,7 +148,7 @@ and overwrites the `lib/` directory. To clean up after generating the coverage
`145`	`148`	`reports:`
`146`	`149`
`147`	`150`	```console
`148`		`-make coverage-clean`
	`151`	`+$ make coverage-clean`
`149`	`152`	```
`150`	`153`
`151`	`154`	`To build the documentation:`