Clarifying the JSON format output

[chinyeungli]

https://github.com/aboutcode-org/scancode-toolkit/blob/develop/docs/source/cli-reference/synopsis.rst?plain=1#L104
It mentions the JSON (--json) format, but the sample uses --json-pp instead. We should consider clarifying the difference between the two options.

Select Category

• Inconsistency
• New Section Request
• General Improvement
• Typo/Mistakes
• Other

[chinyeungli]

Related #2826