fix(docs): clean up npm prefix docs

[wraithgar]

Adds an example and slightly changes wording

References

Closes npm/statusboard#234

[npm-deploy-user]

no statistically significant performance changes detected

timing results

app-large	clean	lock-only	cache-only	cache-only legacy-peer-deps	modules-only	no-lock	no-cache	no-modules	no-clean	no-clean audit
npm@7	45.996 ±0.02	28.146 ±0.09	28.944 ±0.25	27.371 ±0.10	2.151 ±0.02	2.195 ±0.02	1.557 ±0.03	11.001 ±0.00	1.503 ±0.03	3.386 ±0.03
#2463	45.209 ±1.03	28.612 ±0.13	28.279 ±0.71	26.527 ±0.42	2.206 ±0.00	2.146 ±0.01	1.507 ±0.00	10.875 ±0.36	1.583 ±0.02	3.617 ±0.14

app-medium	clean	lock-only	cache-only	cache-only legacy-peer-deps	modules-only	no-lock	no-cache	no-modules	no-clean	no-clean audit
npm@7	31.808 ±0.11	20.269 ±0.03	21.042 ±0.54	18.848 ±0.19	2.126 ±0.04	2.064 ±0.04	1.402 ±0.01	6.587 ±0.15	1.403 ±0.01	2.604 ±0.01
#2463	31.540 ±1.11	19.913 ±0.21	19.422 ±0.15	19.347 ±0.71	2.085 ±0.01	2.075 ±0.03	1.455 ±0.03	6.829 ±0.04	1.416 ±0.01	2.714 ±0.11