docs: Correct place for passing extension option to createMDX()

[eliot-akira]

What?

Fixing a little mistake in the documentation, where the placement of the extension option for createMDX() was described as being inside the options property:

const withMDX = createMDX({
  options: {
    extension: /\.mdx?$/,

But it's actually a property of its own:

const withMDX = createMDX({
  extension: /\.mdx?$/,

I confirmed that the latter is correct because:

• It solves an issue I was having: Unable to import .md files
• On the same docs page, there's another place where it mentions this extension option and the code example is correct there
• The option is described in a similar issue, such as Cannot load plain markdown files using @next/mdx for server components #45431 (comment)

[orca-security-us]

Orca Security Scan Summary

Status	Check	Issues by priority
Passed	Secrets	0   0   0   0	View in Orca

[styfle]

Thanks!