crop option not documented

[s-geiger-si]

The drawio ui has an option called crop for the Export to PDF dialog. The README.md does not mention this option. I tried with --data-urlencode "crop=1" and that worked but would be nice to include this in the readme to safe users some time.

Also maybe add an example for curl such as

curl -X POST http://localhost:8000/ImageExport4/export -H "Content-Type: application/x-www-form-urlencoded" \
    --data-urlencode "format=pdf" --data-urlencode \
    "xml@myfile.drawio.svg" --data-urlencode "filename=myfile.drawio.svg" --data-urlencode "crop=1" --output myfile.pdf