Documentation for Codesigning

[DanielArnett]

My plugin can be run but not distributed on OSX and we believe it's due to an issue with codesigning. I've created an issue ticket for my plugin here. Since we can't run these plugins without Resolume running, and since this is a problem that all plugin developers need to deal with I think these steps need to be laid out in the README for this project.

Please update the README documentation with a description or link to a description on how to codesign a plugin before closing this issue.