[docs] Add precision about pageExtensions

[yoannmoinet]

Adding a precision because when you change the pageExtensions configuration in next.config.js, middleware.ts isn't recognized anymore.

Took me some time to debug this one, not sure if it should be considered a bug or just lack of documentation.
I'll let you be the judge of that.

Documentation / Examples

• Make sure the linting passes by running pnpm lint
• The examples guidelines are followed from our contributing doc

[ijjk]

Hi, I'm not sure we need to document this here as we already explain this under the pageExtensions doc here https://nextjs.org/docs/api-reference/next.config.js/custom-page-extensions

[yoannmoinet]

@ijjk ah! I totally missed it.

I added the middleware way after I touched pageExtensions though, so I didn't go back to the pageExtensions doc when I had an issue with the middleware.

I'm fine closing this, it's just that I figured, if it happened to me, might happen to others.
Feel free to close this.

[ijjk]

Sounds good to add this note, updated to link to the existing pageExtensions doc. Thanks!