Document VM location on disk

Fixes #68

README.md

@@ -178,6 +178,13 @@ tart pull acme.io/remoteorg/name:latest my-local-vm-name
   disk size for new virtual machines. Here is an example of [how to change disk size in a Packer template](https://github.com/cirruslabs/macos-image-templates/blob/fb0bcf68e0b093129136875c050205a66729b596/templates/base.pkr.hcl#L15).
 </details>
 
+<details>
+  <summary>VM location on disk</summary>
+
+  Tart stores all it's files in `~/.tart` directory. Local images that you can run are stored in `~/.tart/vms`.
+  Remote images are pulled into `~/.tart/vms/cache/OCIs/`.
+</details>
+
 <details>
   <summary>Nested virtualization support?</summary>