docs(cli): clarify that --output json requires extraction strategy

[ege-arhan]

Closes #2334

Clarifies in click option help that -o json expects an extraction strategy or schema to be set for structured extractions, preventing user confusion when raw markdown/HTML is returned.

[SohamKukreti]

Thanks for raising this and opening a fix!

A few changes before we can merge:

1. Base branch
This targets main. Please rebase onto develop. All changes go there first.

2. Help text wording
The real behavior is worse than the help text suggests. Without -j or -e, -o json crashes:

$ crwl https://example.com -o json
None
Error: the JSON object must be str, bytes or bytearray, not NoneType

We're fixing the crash in a separate maintainer PR: -o json without an extraction strategy will exit early with a clear error. So the help text just needs to say what json is for. Suggested wording:

json = extracted data only (needs -j or -e). Use 'all' (default) for the full crawl result.

[ege-arhan]

Updated help text to the suggested wording and rebased onto develop. Base branch updated as well.