Update README with raspberry pi instructions
Adds instructions around getting the node to run on newer Raspberry Pi installs, sparked by #45 (closed).
Unfortunately I didn't get the node to work with the Unicam driver. It's probably possible, but not without a good amount of special refactoring just for this case.
Some other slight updates to the readme hitching a ride:
- Start of a list of compatible cameras. Any further suggestions welcome.
- Move the link to the Medium article down. Most people should probably just see the Apt solution first
- Link to image transport plugin source for those that do need to build from source