Update readme.md of next-mdx to allow typescript file extensions for pages

[cmdcolin]

Hi there
I was using the typescript blog template and had some tsx pages. I saw they stopped working after using the mdx recommended here, but adding the tsx and ts extensions restored it.

This PR proposes just listing ts and tsx in the allowed extensions. It could conditionally mention only adding those if using typescript but may be ok like this?

Let me know what you think

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall decrease ✓

	vercel/next.js canary	cmdcolin/next.js patch-1	Change
buildDuration	13.8s	13.9s	⚠️ +106ms
buildDurationCached	3.1s	3.1s	⚠️ +17ms
nodeModulesSize	348 MB	348 MB	-7 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	cmdcolin/next.js patch-1	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.767	2.741	-0.03
/ avg req/sec	903.66	912.02	+8.36
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.15	1.181	⚠️ +0.03
/error-in-render avg req/sec	2174.43	2116.28	⚠️ -58.15

Client Bundles (main, webpack, commons)

	vercel/next.js canary	cmdcolin/next.js patch-1	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	27 kB	27 kB	✓
webpack-HASH.js gzip	1.45 kB	1.45 kB	✓
Overall change	70.9 kB	70.9 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	cmdcolin/next.js patch-1	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	cmdcolin/next.js patch-1	Change
_app-HASH.js gzip	1.37 kB	1.37 kB	✓
_error-HASH.js gzip	194 B	194 B	✓
amp-HASH.js gzip	312 B	312 B	✓
css-HASH.js gzip	326 B	326 B	✓
dynamic-HASH.js gzip	2.37 kB	2.37 kB	✓
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	919 B	919 B	✓
image-HASH.js gzip	4.73 kB	4.73 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	2.13 kB	2.13 kB	✓
routerDirect..HASH.js gzip	321 B	321 B	✓
script-HASH.js gzip	383 B	383 B	✓
withRouter-HASH.js gzip	318 B	318 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	14.1 kB	14.1 kB	✓

Client Build Manifests

	vercel/next.js canary	cmdcolin/next.js patch-1	Change
_buildManifest.js gzip	459 B	459 B	✓
Overall change	459 B	459 B	✓

Rendered Page Sizes

	vercel/next.js canary	cmdcolin/next.js patch-1	Change
index.html gzip	533 B	533 B	✓
link.html gzip	546 B	546 B	✓
withRouter.html gzip	528 B	528 B	✓
Overall change	1.61 kB	1.61 kB	✓

---

Default Build with SWC (Increase detected ⚠️)

General Overall decrease ✓

	vercel/next.js canary	cmdcolin/next.js patch-1	Change
buildDuration	15.3s	15.3s	⚠️ +11ms
buildDurationCached	3.1s	3.1s	-2ms
nodeModulesSize	348 MB	348 MB	-7 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	cmdcolin/next.js patch-1	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.71	2.722	⚠️ +0.01
/ avg req/sec	922.39	918.3	⚠️ -4.09
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.153	1.147	-0.01
/error-in-render avg req/sec	2168.16	2179.02	+10.86

Client Bundles (main, webpack, commons)

	vercel/next.js canary	cmdcolin/next.js patch-1	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.3 kB	42.3 kB	✓
main-HASH.js gzip	27.2 kB	27.2 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	71.1 kB	71.1 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	cmdcolin/next.js patch-1	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	cmdcolin/next.js patch-1	Change
_app-HASH.js gzip	1.35 kB	1.35 kB	✓
_error-HASH.js gzip	180 B	180 B	✓
amp-HASH.js gzip	305 B	305 B	✓
css-HASH.js gzip	321 B	321 B	✓
dynamic-HASH.js gzip	2.36 kB	2.36 kB	✓
head-HASH.js gzip	342 B	342 B	✓
hooks-HASH.js gzip	906 B	906 B	✓
image-HASH.js gzip	4.75 kB	4.75 kB	✓
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	2.19 kB	2.19 kB	✓
routerDirect..HASH.js gzip	314 B	314 B	✓
script-HASH.js gzip	375 B	375 B	✓
withRouter-HASH.js gzip	309 B	309 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	14.1 kB	14.1 kB	✓

Client Build Manifests

	vercel/next.js canary	cmdcolin/next.js patch-1	Change
_buildManifest.js gzip	458 B	458 B	✓
Overall change	458 B	458 B	✓

Rendered Page Sizes

	vercel/next.js canary	cmdcolin/next.js patch-1	Change
index.html gzip	532 B	532 B	✓
link.html gzip	545 B	545 B	✓
withRouter.html gzip	525 B	525 B	✓
Overall change	1.6 kB	1.6 kB	✓

Commit: fa0c6c8