Update readme to link to the new docs

[lfades]

I'm not adding a link to the old readme for the following reasons:

• The new docs are better and the old docs will not receive more updates
• The Next.js docs have a banner at the top with a link to the old docs, temporarily

[ijjk]

Stats from current PR

Default Server Mode (Decrease detected ✓)

General Overall decrease ✓

	zeit/next.js canary	lfades/next.js update-main-readme	Change
buildDuration	12.2s	12.2s	-78ms
nodeModulesSize	49 MB	48.9 MB	-94.4 kB

Client Bundles (main, webpack, commons)

	zeit/next.js canary	lfades/next.js update-main-readme	Change
main-HASH.js gzip	5.11 kB	5.11 kB	✓
webpack-HASH.js gzip	746 B	746 B	✓
4952ddcd88e7..54d3.js gzip	4.68 kB	4.68 kB	✓
commons.HASH.js gzip	4.06 kB	4.06 kB	✓
de003c3a9d30..e54b.js gzip	13.7 kB	13.7 kB	✓
framework.HASH.js gzip	39.1 kB	39.1 kB	✓
Overall change	67.5 kB	67.5 kB	✓

Client Bundles (main, webpack, commons) Modern

	zeit/next.js canary	lfades/next.js update-main-readme	Change
main-HASH.module.js gzip	4.17 kB	4.17 kB	✓
webpack-HASH..dule.js gzip	746 B	746 B	✓
4952ddcd88e7..dule.js gzip	5.56 kB	5.56 kB	✓
de003c3a9d30..dule.js gzip	12.5 kB	12.5 kB	✓
framework.HA..dule.js gzip	39.1 kB	39.1 kB	✓
Overall change	62.1 kB	62.1 kB	✓

Legacy Client Bundles (polyfills)

	zeit/next.js canary	lfades/next.js update-main-readme	Change
polyfills-HASH.js gzip	4.76 kB	4.76 kB	✓
Overall change	4.76 kB	4.76 kB	✓

Client Pages

	zeit/next.js canary	lfades/next.js update-main-readme	Change
_app.js gzip	1.33 kB	1.33 kB	✓
_error.js gzip	4.07 kB	4.07 kB	✓
hooks.js gzip	779 B	779 B	✓
index.js gzip	222 B	222 B	✓
link.js gzip	2.9 kB	2.9 kB	✓
routerDirect.js gzip	283 B	283 B	✓
withRouter.js gzip	282 B	282 B	✓
Overall change	9.87 kB	9.87 kB	✓

Client Pages Modern

	zeit/next.js canary	lfades/next.js update-main-readme	Change
_app.module.js gzip	757 B	757 B	✓
_error.module.js gzip	3.06 kB	3.06 kB	✓
hooks.module.js gzip	371 B	371 B	✓
index.module.js gzip	212 B	212 B	✓
link.module.js gzip	2.47 kB	2.47 kB	✓
routerDirect..dule.js gzip	273 B	273 B	✓
withRouter.m..dule.js gzip	272 B	272 B	✓
Overall change	7.41 kB	7.41 kB	✓

Client Build Manifests

	zeit/next.js canary	lfades/next.js update-main-readme	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	lfades/next.js update-main-readme	Change
index.html gzip	1.02 kB	1.02 kB	✓
link.html gzip	1.03 kB	1.03 kB	✓
withRouter.html gzip	1.02 kB	1.02 kB	✓
Overall change	3.07 kB	3.07 kB	✓

---

Serverless Mode (Decrease detected ✓)

General Overall decrease ✓

	zeit/next.js canary	lfades/next.js update-main-readme	Change
buildDuration	12.9s	12.6s	-297ms
nodeModulesSize	49 MB	48.9 MB	-94.4 kB

Client Bundles (main, webpack, commons)

	zeit/next.js canary	lfades/next.js update-main-readme	Change
main-HASH.js gzip	5.11 kB	5.11 kB	✓
webpack-HASH.js gzip	746 B	746 B	✓
4952ddcd88e7..54d3.js gzip	4.68 kB	4.68 kB	✓
commons.HASH.js gzip	4.06 kB	4.06 kB	✓
de003c3a9d30..e54b.js gzip	13.7 kB	13.7 kB	✓
framework.HASH.js gzip	39.1 kB	39.1 kB	✓
Overall change	67.5 kB	67.5 kB	✓

Client Bundles (main, webpack, commons) Modern

	zeit/next.js canary	lfades/next.js update-main-readme	Change
main-HASH.module.js gzip	4.17 kB	4.17 kB	✓
webpack-HASH..dule.js gzip	746 B	746 B	✓
4952ddcd88e7..dule.js gzip	5.56 kB	5.56 kB	✓
de003c3a9d30..dule.js gzip	12.5 kB	12.5 kB	✓
framework.HA..dule.js gzip	39.1 kB	39.1 kB	✓
Overall change	62.1 kB	62.1 kB	✓

Legacy Client Bundles (polyfills)

	zeit/next.js canary	lfades/next.js update-main-readme	Change
polyfills-HASH.js gzip	4.76 kB	4.76 kB	✓
Overall change	4.76 kB	4.76 kB	✓

Client Pages

	zeit/next.js canary	lfades/next.js update-main-readme	Change
_app.js gzip	1.33 kB	1.33 kB	✓
_error.js gzip	4.07 kB	4.07 kB	✓
hooks.js gzip	779 B	779 B	✓
index.js gzip	222 B	222 B	✓
link.js gzip	2.9 kB	2.9 kB	✓
routerDirect.js gzip	283 B	283 B	✓
withRouter.js gzip	282 B	282 B	✓
Overall change	9.87 kB	9.87 kB	✓

Client Pages Modern

	zeit/next.js canary	lfades/next.js update-main-readme	Change
_app.module.js gzip	757 B	757 B	✓
_error.module.js gzip	3.06 kB	3.06 kB	✓
hooks.module.js gzip	371 B	371 B	✓
index.module.js gzip	212 B	212 B	✓
link.module.js gzip	2.47 kB	2.47 kB	✓
routerDirect..dule.js gzip	273 B	273 B	✓
withRouter.m..dule.js gzip	272 B	272 B	✓
Overall change	7.41 kB	7.41 kB	✓

Client Build Manifests

	zeit/next.js canary	lfades/next.js update-main-readme	Change
_buildManifest.js gzip	61 B	61 B	✓
_buildManife..dule.js gzip	61 B	61 B	✓
Overall change	122 B	122 B	✓

Serverless bundles

	zeit/next.js canary	lfades/next.js update-main-readme	Change
_error.js gzip	77.8 kB	77.8 kB	✓
hooks.html gzip	1.06 kB	1.06 kB	✓
index.js gzip	78 kB	78 kB	✓
link.js gzip	80.4 kB	80.4 kB	✓
routerDirect.js gzip	78.1 kB	78.1 kB	✓
withRouter.js gzip	78.1 kB	78.1 kB	✓
Overall change	393 kB	393 kB	✓

Commit: f904abb