Correct DOI file argument messages

[Mirochill]

Summary

• Replace the stale --file reference in the missing-input CLI error with the actual --doi-file and --doi options.
• Clarify that --scholar-pages is required for both --query and --cites paths.
• Align the README note with the parser's accepted entry arguments.

Fixes #51

Validation

• git diff --check
• git diff --cached --check
• git diff --check HEAD~1..HEAD
• git show --check --stat --oneline HEAD
• Not run locally