Revise documentation to update version flag
Revise documentation to update version flag

The documentation referenced `-v` to show version, but this gave an error currently; this updates this one line of the documentation to use the `--version` option (which then gives the version as expected).
poldracklab/mriqc,poldracklab/mriqc,oesteban/mriqc,poldracklab/mriqc,oesteban/mriqc,oesteban/mriqc,oesteban/mriqc,poldracklab/mriqc