docs: add jsonschema step inside the new linters doc

[uudashr]

Add guideline to modify jsonschema/golangci.next.jsonschema.json for new linter

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[ldez]

I consider updating the JSON Schema as optional because it requires different knowledge.

This is why it's not inside the doc and only an option inside the checklist.

[uudashr]

Been thinking so because is not in the guidline. But when I run the test against the project, it failed.