[µTVM] Minor fixes to the Reference VM tutorial (apache#7012)

* Add recommendation to install vbguest plugin.

* Update directories to match checked-in.

tutorials/micro/micro_reference_vm.py

@@ -61,7 +61,8 @@
 1. `Vagrant <https://vagrantup.com>`__
 2. A supported Virtual Machine hypervisor.
    `VirtualBox <https://www.virtualbox.org>`__ is one suggested free hypervisor, but please note
-   that the `VirtualBox Extension Pack`_ is required for proper USB forwarding.
+   that the `VirtualBox Extension Pack`_ is required for proper USB forwarding. If using VirtualBox,
+   also consider installing the `vbguest <https://github.com/dotless-de/vagrant-vbguest>`_ plugin.
 
 .. _VirtualBox Extension Pack: https://www.virtualbox.org/wiki/Downloads#VirtualBox6.1.16OracleVMVirtualBoxExtensionPack
 
@@ -72,9 +73,10 @@
 
 .. code-block:: bash
 
-    ~/.../tvm $ cd apps/microtvm-vm
+    # Replace zepyhr with the name of a different platform, if you are not using Zephyr.
+    ~/.../tvm $ cd apps/microtvm/reference-vm/zephyr
     # Replace <provider_name> with the name of the hypervisor you wish to use (i.e. virtualbox).
-    ~/.../tvm/apps/microtvm/vm $ vagrant up --provider=<provider_name>
+    ~/.../tvm/apps/microtvm/reference-vm/zephyr $ vagrant up --provider=<provider_name>
 
 
 This command will take a couple of minutes to run and will require 4 to 5GB of storage on your