Added osxphotos docs command

[RhetTbull]

Version v0.47.8 adds a new osxphotos docs command which opens the osxphotos documentation in your browser (from a local cached copy). The docs are fully searchable. Hopefully this will make it easier to reference the documentation than from the command line using osxphotos help. You can see a preview of the documentation that will be opened with osxphotos docs here.