Dune: Document how to disable warning-as-errors

[XVilka]

Wasn't able to find any mention of this in the documentation, I had some warnings when using jbuilder, was just ignoring them, after migration to dune it enforces them as errors. I believe many people will meet this problem upon conversion.

[emillon]

It's true that it's a bit hidden in the documentation at the moment.

You can disable that behavior by passing --profile release to dune.

Note that dune still ships a jbuilder binary that ignores warnings by default, so this means that you can convert your jbuild files to dune files, while continuing to use the jbuilder executable which will ignore the warnings.

[rgrinberg]

Perhaps we can add this in the FAQ?