Please mention SVG output option in usage summary

[rrthomas]

The usage summary currently says:

Usage: qrencode [-o FILENAME] [OPTION]... [STRING]
Encode input data in a QR Code and save as a PNG or EPS image.

Please also mention SVG output here! I didn't realise that qrencode could output SVG, until I looked carefully at --help's output, as the Debian package description doesn't mention this functionality either.

Thank you for qrencode!