Fixed typos in QUICKSTART.md

I've found out trivial typos in QUICKSTART.md.
Please check the line 104, 124, and 128.

    104     $ sudo ${RTE_SDK}/tools/pci_unbind.py --status

    124     $ sudo ${RTE_SDK}/pci_unbind.py -b igb_uio 0000:02:02.0 0000:02:03.0 0000:02:04.0

    128     $ sudo ${RTE_SDK}/pci_unbind.py --status

Since "pci_unbind.py" is located in the ${RTE_SDK}/tools/, the line 124 and 128 should be fixed.