[pyos][docs] `--input-type` not mentioned in "converting between formats"

[sneakers-the-rat]

Part of: pyOpenSci/software-submission#267 (comment)

User is shown an example of giving input in .bib format:

OneCite/docs/advanced_usage.rst

Line 130 in 12b1dea

onecite process input.bib --output-format apa -o output.txt

however without explicitly passing --input-type bib, the input is parsed as text:

OneCite/onecite/pipeline.py

Line 61 in 12b1dea

return self._parse_text(input_content)