docs(readme): add note about not supporting Node.js 7
docs(readme): add note about not supporting Node.js 7

Signed-off-by: Andrew Koroluk <0525fd2e888f436078c8e9bcae4607e72e217fa0@gmail.com>
Signed-off-by: Brendan Le Foll <3e0e8c4069934e8b47d99704927a85c66c0ceb33@intel.com>

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