add back vagrant virtualbox wsl2 plugin

have not tested without the plugin installed

README.md

@@ -82,6 +82,7 @@ Importantly:
 
 - Work on a folder on the windows file system.
 - Export VAGRANT_WSL_WINDOWS_ACCESS_USER_HOME_PATH="/mnt/c/.../infra"
+- Install vagrant plugin https://github.com/Karandash8/virtualbox_WSL2
 - `export PATH="$PATH:C:\Program Files\Oracle\VirtualBox"`
 - ` vagrant up --provider virtualbox`
 - Approve the firewall popup