fix(docs): clean up npm stop docs

[wraithgar]

Adds an example and outlines differences with npm start

References

Closes npm/statusboard#248

[npm-deploy-user]

	angular-quickstart			app-large			app-medium			ember-quickstart			react-app
	prev	current	status	prev	current	status	prev	current	status	prev	current	status	prev	current	status
initial install	41s	47s	🛑	39.5s	50.5s	🛑	34.5s	37s	✅🐌	28.1s	32.6s	🛑	33.5s	42.2s	🛑
repeat install	9.6s	3.6s	✅	8.6s	4.2s	✅	8.3s	2.9s	✅	7.7s	2s	✅	9.1s	3.1s	✅
with warm cache	32.3s	26.2s	✅	33.8s	33.6s	✅	31.3s	22s	✅	23.4s	21.4s	✅	29.1s	22.9s	✅
with node_modules	9.2s	6.4s	✅	8.6s	5.3s	✅	9s	3.9s	✅	7.8s	2.2s	✅	9.4s	6.5s	✅
with lockfile	32.6s	33s	✅🐌	31s	34s	✅🐌	29s	23.2s	✅	21.7s	19.9s	✅	27.4s	28.9s	✅🐌
with warm cache and node_modules	9.3s	3.9s	✅	7.9s	4.1s	✅	8.4s	3.4s	✅	7.6s	2.1s	✅	9.2s	3.4s	✅
with warm cache and lockfile	24.7s	11.5s	✅	26.3s	14.6s	✅	24.3s	9.1s	✅	17.8s	7.3s	✅	21.3s	8.6s	✅
with node_modules and lockfile	10.1s	6s	✅	9.8s	4.8s	✅	8.6s	4.5s	✅	7.8s	1.9s	✅	9.7s	6.2s	✅