minor warning about upgrading to Monterey

Author: myspaghetti

README.md

@@ -9,7 +9,7 @@ A default install only requires the user to sit patiently and, less than ten tim
 
 Tested on `bash` and `zsh` on [Cygwin](https://cygwin.com/install.html). Works on macOS, CentOS 7, and Windows. Should work on most modern Linux distros.
 
-macOS Catalina (10.15), Mojave (10.14), and High Sierra (10.13) currently supported. The virtual machine may be upgraded to the latest Big Sur (11) and Monterey (12) versions through Software Update.
+macOS Catalina (10.15), Mojave (10.14), and High Sierra (10.13) currently supported.
 
 ## Documentation
 
@@ -37,6 +37,10 @@ Developing and maintaining VirtualBox or macOS features is beyond the scope of t
 
 macOS guests on VirtualBox are incompatible with some CPU models. If the guest macOS boot process hangs on “LoadKernelFromStream”, “EndRandomSeed”, or "EXITBS", see the [documentation command](#documentation) regarding VirtualBox CPU profiles and [CPUID settings](https://www.virtualbox.org/manual/ch08.html#vboxmanage-modifyvm-teleport). Some CPU models released in 2020 and later may fail to start or complete the installer, and may require manually adjusting the CPUID settings.
 
+### Upgrading to Big Sur and Monterey 
+
+The virtual machine may be upgraded to the latest Big Sur (11) and Monterey (12) versions through Software Update, though it's probably quicker and less failure-prone to create a bootable installation volume with [`createinstallmedia --downloadassets`](https://support.apple.com/en-us/HT201372) and use it to upgrade the existing macOS installation or create a new one.
+
 ### Performance and deployment
 
 After successfully creating a working macOS virtual machine, consider importing it into more performant virtualization software, or packaging it for configuration management platforms for automated deployment. These virtualization and deployment applications require additional configuration that is beyond the scope of the script.