fix(docs): Clarify contribution docs about linting

[lobsterkatie]

While making my first PR to this repo recently, I came across this instruction:

• Make sure the linting passes

and while I was guessing that yarn lint would do it, I wanted to confirm, so I headed over to CONTRIBUTING.md and searched for "lint," but found nothing. So I checked out package.json, found out what I needed to know, linted, pushed, and was on my way.

Not that hard. But why not make it easier? :-)

This PR includes two main changes:

• The instruction above is amended with the command to do the linting
• There is a "Linting" section added to CONTRIBUTING.md

While I was in the latter document, I noticed two other things which I thought could potentially be clearer and fixed those, too:

• In the testing section, when talking about testing a particular suite of tests, the example suite is "production". Since that word is so overloaded, I added an "e.g." to make it clear that it's just an example test suite name and doesn't have any other special meaning.
• In the section about testing against the examples, I changed the title to use "examples," since that's how they're talked about everywhere else that I've seen, both in the docs and in the repo.

(These latter two I don't feel strongly about, and are admittedly out of scope for this PR, so if you want me to revert them, I can, as they're really just drive-bys.)

[ijjk]

Thanks!

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	lobsterkatie/next.js kmclb-clarify-linting-in-dev	Change
buildDuration	11.9s	12.3s	⚠️ +430ms
buildDurationCached	2.7s	2.6s	-60ms
nodeModulesSize	195 MB	195 MB	⚠️ +7 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	lobsterkatie/next.js kmclb-clarify-linting-in-dev	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.864	2.86	0
/ avg req/sec	872.77	874.15	+1.38
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.379	1.397	⚠️ +0.02
/error-in-render avg req/sec	1813.27	1790.12	⚠️ -23.15

Client Bundles (main, webpack, commons)

	vercel/next.js canary	lobsterkatie/next.js kmclb-clarify-linting-in-dev	Change
651.cd440d20..0b23.js gzip	2.96 kB	2.96 kB	✓
831.695e33f6..205f.js gzip	179 B	179 B	✓
framework-89..a097.js gzip	42.2 kB	42.2 kB	✓
main-45201df..96b4.js gzip	26.1 kB	26.1 kB	✓
webpack-f09b..493e.js gzip	1.47 kB	1.47 kB	✓
Overall change	73 kB	73 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	lobsterkatie/next.js kmclb-clarify-linting-in-dev	Change
polyfills-a4..dd70.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	lobsterkatie/next.js kmclb-clarify-linting-in-dev	Change
_app-9fb8765..c13d.js gzip	979 B	979 B	✓
_error-d828d..2954.js gzip	3.06 kB	3.06 kB	✓
amp-5388d1f5..4ce9.js gzip	551 B	551 B	✓
css-10424225..367a.js gzip	329 B	329 B	✓
dynamic-9821..3cd4.js gzip	2.67 kB	2.67 kB	✓
head-1df323b..d261.js gzip	2.32 kB	2.32 kB	✓
hooks-ab0016..b093.js gzip	917 B	917 B	✓
image-c3cc30..4e2a.js gzip	5.87 kB	5.87 kB	✓
index-95c8cb..6970.js gzip	260 B	260 B	✓
link-05c99e7..35ec.js gzip	1.66 kB	1.66 kB	✓
routerDirect..6659.js gzip	319 B	319 B	✓
script-d94ba..ed05.js gzip	386 B	386 B	✓
withRouter-7..8b2e.js gzip	317 B	317 B	✓
9a34b27eb3f9..27d.css gzip	125 B	125 B	✓
Overall change	19.8 kB	19.8 kB	✓

Client Build Manifests

	vercel/next.js canary	lobsterkatie/next.js kmclb-clarify-linting-in-dev	Change
_buildManifest.js gzip	458 B	458 B	✓
Overall change	458 B	458 B	✓

Rendered Page Sizes

	vercel/next.js canary	lobsterkatie/next.js kmclb-clarify-linting-in-dev	Change
index.html gzip	537 B	537 B	✓
link.html gzip	549 B	549 B	✓
withRouter.html gzip	529 B	529 B	✓
Overall change	1.61 kB	1.61 kB	✓

---

Default Build with SWC (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	lobsterkatie/next.js kmclb-clarify-linting-in-dev	Change
buildDuration	5.6s	5.8s	⚠️ +193ms
buildDurationCached	2.7s	2.5s	-125ms
nodeModulesSize	195 MB	195 MB	⚠️ +7 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	lobsterkatie/next.js kmclb-clarify-linting-in-dev	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.622	2.69	⚠️ +0.07
/ avg req/sec	953.64	929.22	⚠️ -24.42
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.29	1.341	⚠️ +0.05
/error-in-render avg req/sec	1938.72	1864.74	⚠️ -73.98

Client Bundles (main, webpack, commons)

	vercel/next.js canary	lobsterkatie/next.js kmclb-clarify-linting-in-dev	Change
450.fd3ad245..022b.js gzip	179 B	179 B	✓
675-f623fa2a..036a.js gzip	13.9 kB	13.9 kB	✓
framework-13..70b0.js gzip	50.8 kB	50.8 kB	✓
main-1e4b9db..ad07.js gzip	36.5 kB	36.5 kB	✓
webpack-a7f2..2650.js gzip	1.63 kB	1.63 kB	✓
Overall change	103 kB	103 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	lobsterkatie/next.js kmclb-clarify-linting-in-dev	Change
polyfills-a4..dd70.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	lobsterkatie/next.js kmclb-clarify-linting-in-dev	Change
_app-ae91bc3..d985.js gzip	1.33 kB	1.33 kB	✓
_error-273ac..9ef0.js gzip	180 B	180 B	✓
amp-5f9a7694..99ce.js gzip	315 B	315 B	✓
css-3a1b2477..df1e.js gzip	330 B	330 B	✓
dynamic-8d0e..e365.js gzip	2.79 kB	2.79 kB	✓
head-7f600d0..daa3.js gzip	356 B	356 B	✓
hooks-bd8c02..0730.js gzip	638 B	638 B	✓
image-16df09..4584.js gzip	555 B	555 B	✓
index-80be94..e89f.js gzip	262 B	262 B	✓
link-4ee1ea7..8745.js gzip	2.22 kB	2.22 kB	✓
routerDirect..c4aa.js gzip	325 B	325 B	✓
script-67da0..49e6.js gzip	390 B	390 B	✓
withRouter-2..2409.js gzip	322 B	322 B	✓
9a34b27eb3f9..27d.css gzip	125 B	125 B	✓
Overall change	10.1 kB	10.1 kB	✓

Client Build Manifests

	vercel/next.js canary	lobsterkatie/next.js kmclb-clarify-linting-in-dev	Change
_buildManifest.js gzip	476 B	476 B	✓
Overall change	476 B	476 B	✓

Rendered Page Sizes

	vercel/next.js canary	lobsterkatie/next.js kmclb-clarify-linting-in-dev	Change
index.html gzip	534 B	534 B	✓
link.html gzip	545 B	545 B	✓
withRouter.html gzip	526 B	526 B	✓
Overall change	1.6 kB	1.6 kB	✓

Commit: 45d9956