add VM configuration to install instructions

It is often helpful to know what resources the VM takes by default, in
particular if you are on an older laptop/work station.

INSTALL.md

@@ -11,7 +11,8 @@ Get Quantum Mobile running on your computer in three simple steps:
  3. Import virtual machine image into Virtualbox (${vm_vdisk_size})
     File => Import Appliance
 
-Note: username: `${vm_user}`, password: `${vm_password}`
+Login credentials: username: `${vm_user}`, password: `${vm_password}`.  
+The default configuration of `${vm_cpus}` cores and `${vm_memory}` MB RAM can be adjusted in the VM settings.
 
 
 ## Contact