add a note that VMs can be deleted ...

re #4

README.md

@@ -14,7 +14,7 @@ Replicate Slicer running GCP machine with instructions and write them down for t
 * Be careful with your login information.  If someone takes over your account they **could run up a huge bill that you will be responsible for paying**.
 * Depending on your specific situation, not all of the options or steps may be available or applicable (e.g., as a member of organization, your organization administrator may have disabled some of the options discussed).
 * Unless you are not concerned about billing, remember to **SHUT DOWN THE MACHINE** when you aren't using it! You are billed continuously while the VM instance is running.
-* Even after you stop the VMs, you keep paying for the disk storage attached to those machines!
+* Even after you stop the VMs, you keep paying for the disk storage attached to those machines! You can delete the VM instances to stop incurring those costs.
 
 ## Instructions