Add relevant information to README; move notes to NOTES.rst.
Add a test to do guestfish (libguestfs) baseline performance to give an
indication of overhead of nested virtualization. guestfish

    Refer: http://libguestfs.org/guestfs-performance.1.html

To summarize (as of writing this):

     L0 (bare-metal):
        - guestfish run: ~ 3 seconds

     L1 (guest):
        - w/o nesting, guestfish run: ~ 52 seconds
        - w/ nesting,  guestfish run: ~ 8 seconds  (Almost 6 1/2 times speed improvement)

Clarification:

    "w/ nesting" means L1's qemu-kvm CLI will have:
       -cpu Haswell,+vmx  # or whatever the model is

    "w/o nesting" means no `-cpu` parameter in L1's qemu-kvm CLI.
Add some initial notes and simple tests to do kernel builds inside L2
(nested guest).
Update TODO.rst; add a couple more tests to nested-vmx-tests.rst