Document deploying Coder Desktop for macOS over MDM

There's a few things that MDM admins need to do to get Coder Desktop working over MDM, these include:
- Ensuring the package installer runs as root (this might always be the case in MDM, will need to check)
- Pre-approving the Network Extension bundle. This is done by supplying the extension identifier (`com.coder.Coder-Desktop.VPN`)
- Disabling the built-in updater. This is done by forcibly setting the value of `disableUpdater` in the app's userdefaults plist. Support for this was added in #219.

Start by checking how MDM handles package installation and reviewing the deployment-related material already present in the repository. Document running the installer as root, pre-approving the Network Extension identifier com.coder.Coder-Desktop.VPN, and setting disableUpdater in the app's userdefaults plist; done means an MDM administrator can follow the documented deployment steps.

Scritto dal modello di indicizzazione a partire dal testo della issue.