Clarify using netlify dev when importing @netlify/next in docs

[sarahetter]

Related: #2003

User is getting an error if they run next dev when using our advanced middleware - we should make it clear in the documentation for @netlify/next that you must run netlify dev and not next dev because of the edge function.

[MarcL]

Should we move this to https://github.com/netlify/docs now @sarahetter?
We moved to the docs site as being the source of truth for the Next runtime.
Or should this be in the README?

[nickytonline]

I think the general advice should be always run netlify dev. Usually people run next dev to compare regular Next development mode and Netlify development mode if they run into issues.

[sarahetter]

Should we move this to https://github.com/netlify/docs now @sarahetter? We moved to the docs site as being the source of truth for the Next runtime. Or should this be in the README?

This isn't for the runtime, it's for the next package - our advanced middleware

[MarcL]

Ok - The docs for the next package also point to the docs site from the README.
It feels like that should still be the source of truth.

[serhalp]

Superseded by v5. Please feel free to reopen if this is still valid.