Sign macos prebuilds

[Stefterv]

Signing the macOS pre-builds so we can test pre-releases on our own machines. Unfortunately signing the application is not enough and we need to notarise it if we want it to be able to be run. From here we have two options:

• Notarise pre-builds anyway, I dislike this option as it allows for unverified software to be distributed by under the Processing Foundation's name
• Instruct people to use the following hack: xattr -d com.apple.quarantine ./Processing.app this is a more advanced use case but the people who need to check beta software could be expected to jump through this hoop...

If anyone has any input let me know

[SableRaf]

Thanks, @Stefterv! I think the xattr -d com.apple.quarantine workaround is the way to go. We could include this information in a dedicated INSTRUCTIONS_FOR_TESTING file specifically for test builds. What do you think?