Readme updates part 3

[omarcostahamido]

• add readme notes about RPI hdmi 1 and 2.
• add readme note on the incompatibility of omx with prores422 (needs a lot more testing though!)
  • can I get anyone @here to test this please?
• re-arrange readme so that it is clear that installation is not complete without the omx building process
• add readme notes on setting vnc to autostart
  • related link perhaps: https://help.realvnc.com/hc/en-us/articles/360002249917-VNC-Connect-and-Raspberry-Pi#setting-up-your-raspberry-pi-0-0
• add section notes on the steps to update the code base without having to delete entire folder and rebuild everything.
  • this will be mostly terminal git commands that will also include instructions on how to discard changes that have been made since the fork.
  • this may also require updating the .gitignore file to make sure it will not tag omx build files as changes