Add routing example with dynamic as prop

[karlhorky]

Inspired by the dynamic as prop example in the next/link documentation and seeing that this pattern was not in any of the docs pages under Routing, I thought it may be a good idea to surface this common, useful pattern in the regular Routing documentation intro.

If you have a different idea of where to put it within the Routing section, glad to move it too!

[ijjk]

Stats from current PR

Default Server Mode

General

	zeit/next.js canary	karlhorky/next.js patch-1	Change
buildDuration	11.4s	11.2s	-193ms
nodeModulesSize	54.8 MB	54.8 MB	✓

Client Bundles (main, webpack, commons)

	zeit/next.js canary	karlhorky/next.js patch-1	Change
main-HASH.js gzip	5.77 kB	5.77 kB	✓
webpack-HASH.js gzip	746 B	746 B	✓
de003c3a9d30..8eb0.js gzip	9.78 kB	9.78 kB	✓
framework.HASH.js gzip	39.1 kB	39.1 kB	✓
Overall change	55.4 kB	55.4 kB	✓

Client Bundles (main, webpack, commons) Modern

	zeit/next.js canary	karlhorky/next.js patch-1	Change
main-HASH.module.js gzip	4.78 kB	4.78 kB	✓
webpack-HASH..dule.js gzip	746 B	746 B	✓
de003c3a9d30..dule.js gzip	6.71 kB	6.71 kB	✓
framework.HA..dule.js gzip	39.1 kB	39.1 kB	✓
Overall change	51.4 kB	51.4 kB	✓

Legacy Client Bundles (polyfills)

	zeit/next.js canary	karlhorky/next.js patch-1	Change
polyfills-HASH.js gzip	26.3 kB	26.3 kB	✓
Overall change	26.3 kB	26.3 kB	✓

Client Pages

	zeit/next.js canary	karlhorky/next.js patch-1	Change
_app.js gzip	1.09 kB	1.09 kB	✓
_error.js gzip	2.97 kB	2.97 kB	✓
hooks.js gzip	664 B	664 B	✓
index.js gzip	222 B	222 B	✓
link.js gzip	1.89 kB	1.89 kB	✓
routerDirect.js gzip	279 B	279 B	✓
withRouter.js gzip	278 B	278 B	✓
Overall change	7.39 kB	7.39 kB	✓

Client Pages Modern

	zeit/next.js canary	karlhorky/next.js patch-1	Change
_app.module.js gzip	594 B	594 B	✓
_error.module.js gzip	2.08 kB	2.08 kB	✓
hooks.module.js gzip	370 B	370 B	✓
index.module.js gzip	212 B	212 B	✓
link.module.js gzip	1.48 kB	1.48 kB	✓
routerDirect..dule.js gzip	271 B	271 B	✓
withRouter.m..dule.js gzip	270 B	270 B	✓
Overall change	5.28 kB	5.28 kB	✓

Client Build Manifests

	zeit/next.js canary	karlhorky/next.js patch-1	Change
_buildManifest.js gzip	61 B	61 B	✓
_buildManife..dule.js gzip	61 B	61 B	✓
Overall change	122 B	122 B	✓

Rendered Page Sizes

	zeit/next.js canary	karlhorky/next.js patch-1	Change
index.html gzip	916 B	916 B	✓
link.html gzip	924 B	924 B	✓
withRouter.html gzip	911 B	911 B	✓
Overall change	2.75 kB	2.75 kB	✓

---

Serverless Mode (Decrease detected ✓)

General

	zeit/next.js canary	karlhorky/next.js patch-1	Change
buildDuration	12.3s	12.3s	⚠️ +62ms
nodeModulesSize	54.8 MB	54.8 MB	✓

Client Bundles (main, webpack, commons)

	zeit/next.js canary	karlhorky/next.js patch-1	Change
main-HASH.js gzip	5.77 kB	5.77 kB	✓
webpack-HASH.js gzip	746 B	746 B	✓
de003c3a9d30..8eb0.js gzip	9.78 kB	9.78 kB	✓
framework.HASH.js gzip	39.1 kB	39.1 kB	✓
Overall change	55.4 kB	55.4 kB	✓

Client Bundles (main, webpack, commons) Modern

	zeit/next.js canary	karlhorky/next.js patch-1	Change
main-HASH.module.js gzip	4.78 kB	4.78 kB	✓
webpack-HASH..dule.js gzip	746 B	746 B	✓
de003c3a9d30..dule.js gzip	6.71 kB	6.71 kB	✓
framework.HA..dule.js gzip	39.1 kB	39.1 kB	✓
Overall change	51.4 kB	51.4 kB	✓

Legacy Client Bundles (polyfills)

	zeit/next.js canary	karlhorky/next.js patch-1	Change
polyfills-HASH.js gzip	26.3 kB	26.3 kB	✓
Overall change	26.3 kB	26.3 kB	✓

Client Pages

	zeit/next.js canary	karlhorky/next.js patch-1	Change
_app.js gzip	1.09 kB	1.09 kB	✓
_error.js gzip	2.97 kB	2.97 kB	✓
hooks.js gzip	664 B	664 B	✓
index.js gzip	222 B	222 B	✓
link.js gzip	1.89 kB	1.89 kB	✓
routerDirect.js gzip	279 B	279 B	✓
withRouter.js gzip	278 B	278 B	✓
Overall change	7.39 kB	7.39 kB	✓

Client Pages Modern

	zeit/next.js canary	karlhorky/next.js patch-1	Change
_app.module.js gzip	594 B	594 B	✓
_error.module.js gzip	2.08 kB	2.08 kB	✓
hooks.module.js gzip	370 B	370 B	✓
index.module.js gzip	212 B	212 B	✓
link.module.js gzip	1.48 kB	1.48 kB	✓
routerDirect..dule.js gzip	271 B	271 B	✓
withRouter.m..dule.js gzip	270 B	270 B	✓
Overall change	5.28 kB	5.28 kB	✓

Client Build Manifests

	zeit/next.js canary	karlhorky/next.js patch-1	Change
_buildManifest.js gzip	61 B	61 B	✓
_buildManife..dule.js gzip	61 B	61 B	✓
Overall change	122 B	122 B	✓

Serverless bundles Overall decrease ✓

	zeit/next.js canary	karlhorky/next.js patch-1	Change
_error.js gzip	294 kB	293 kB	-459 B
404.html gzip	1.32 kB	1.32 kB	✓
hooks.html gzip	956 B	956 B	✓
index.js gzip	294 kB	293 kB	-271 B
link.js gzip	301 kB	301 kB	-666 B
routerDirect.js gzip	300 kB	300 kB	⚠️ +107 B
withRouter.js gzip	300 kB	299 kB	-473 B
Overall change	1.49 MB	1.49 MB	-1.76 kB

[timneutkens]

Thanks! Hopefully this will help surface that a bit 👍

[karlhorky]

Glad to help :) Thanks for the merge!