Update docs for basePath: false rewrite

[ijjk]

When using rewrites with basePath: false we don't allow the destination to point to an internal location / and require it point to an external location. This makes sure this is noted in the documentation since an error is thrown with the current basePath: false rewrite example.

x-ref: #16958

[ijjk]

Stats from current PR

Default Server Mode (Increase detected ⚠️)

General

	vercel/next.js canary	ijjk/next.js docs/rewrite-basepath-false	Change
buildDuration	8.6s	8.7s	⚠️ +71ms
nodeModulesSize	83 MB	83 MB	✓

Page Load Tests Overall increase ✓

	vercel/next.js canary	ijjk/next.js docs/rewrite-basepath-false	Change
/ failed reqs	0	0	✓
/ total time (seconds)	1.641	1.568	-0.07
/ avg req/sec	1523.16	1594.5	+71.34
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.007	1.03	⚠️ +0.02
/error-in-render avg req/sec	2482.04	2426.57	⚠️ -55.47

Client Bundles (main, webpack, commons)

	vercel/next.js canary	ijjk/next.js docs/rewrite-basepath-false	Change
677f882d2ed8..2428.js gzip	12.9 kB	12.9 kB	✓
framework.HASH.js gzip	39 kB	39 kB	✓
main-212f85f..f23b.js gzip	6.59 kB	6.59 kB	✓
webpack-7193..1446.js gzip	751 B	751 B	✓
Overall change	59.2 kB	59.2 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	ijjk/next.js docs/rewrite-basepath-false	Change
polyfills-67..b7d1.js gzip	31.2 kB	31.2 kB	✓
Overall change	31.2 kB	31.2 kB	✓

Client Pages

	vercel/next.js canary	ijjk/next.js docs/rewrite-basepath-false	Change
_app-6220e08..9a40.js gzip	1.28 kB	1.28 kB	✓
_error-4b0b5..2c91.js gzip	3.44 kB	3.44 kB	✓
hooks-5f309a..7282.js gzip	887 B	887 B	✓
index-57f580..c562.js gzip	227 B	227 B	✓
link-b862cd7..dba8.js gzip	1.64 kB	1.64 kB	✓
routerDirect..bd82.js gzip	303 B	303 B	✓
withRouter-2..e384.js gzip	302 B	302 B	✓
Overall change	8.08 kB	8.08 kB	✓

Client Build Manifests

	vercel/next.js canary	ijjk/next.js docs/rewrite-basepath-false	Change
_buildManifest.js gzip	321 B	321 B	✓
Overall change	321 B	321 B	✓

Rendered Page Sizes

	vercel/next.js canary	ijjk/next.js docs/rewrite-basepath-false	Change
index.html gzip	617 B	617 B	✓
link.html gzip	622 B	622 B	✓
withRouter.html gzip	610 B	610 B	✓
Overall change	1.85 kB	1.85 kB	✓

---

Serverless Mode

General

	vercel/next.js canary	ijjk/next.js docs/rewrite-basepath-false	Change
buildDuration	9.8s	10.3s	⚠️ +500ms
nodeModulesSize	83 MB	83 MB	✓

Client Bundles (main, webpack, commons)

	vercel/next.js canary	ijjk/next.js docs/rewrite-basepath-false	Change
677f882d2ed8..2428.js gzip	12.9 kB	12.9 kB	✓
framework.HASH.js gzip	39 kB	39 kB	✓
main-212f85f..f23b.js gzip	6.59 kB	6.59 kB	✓
webpack-7193..1446.js gzip	751 B	751 B	✓
Overall change	59.2 kB	59.2 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	ijjk/next.js docs/rewrite-basepath-false	Change
polyfills-67..b7d1.js gzip	31.2 kB	31.2 kB	✓
Overall change	31.2 kB	31.2 kB	✓

Client Pages

	vercel/next.js canary	ijjk/next.js docs/rewrite-basepath-false	Change
_app-6220e08..9a40.js gzip	1.28 kB	1.28 kB	✓
_error-4b0b5..2c91.js gzip	3.44 kB	3.44 kB	✓
hooks-5f309a..7282.js gzip	887 B	887 B	✓
index-57f580..c562.js gzip	227 B	227 B	✓
link-b862cd7..dba8.js gzip	1.64 kB	1.64 kB	✓
routerDirect..bd82.js gzip	303 B	303 B	✓
withRouter-2..e384.js gzip	302 B	302 B	✓
Overall change	8.08 kB	8.08 kB	✓

Client Build Manifests

	vercel/next.js canary	ijjk/next.js docs/rewrite-basepath-false	Change
_buildManifest.js gzip	321 B	321 B	✓
Overall change	321 B	321 B	✓

Serverless bundles

	vercel/next.js canary	ijjk/next.js docs/rewrite-basepath-false	Change
_error.js	1 MB	1 MB	✓
404.html	2.67 kB	2.67 kB	✓
hooks.html	1.92 kB	1.92 kB	✓
index.js	1 MB	1 MB	✓
link.js	1.06 MB	1.06 MB	✓
routerDirect.js	1.05 MB	1.05 MB	✓
withRouter.js	1.05 MB	1.05 MB	✓
Overall change	5.17 MB	5.17 MB	✓

Commit: a8c4783