README: Clarify requirements
README: Clarify requirements

* Add tested versions
* Web server only needed for production

Signed-off-by: Paul Eggleton <737d4dae46a541673d7bf4e0d5b32714b16528d8@linux.intel.com>

bartosh/layerindex-web,bartosh/layerindex-web,bartosh/layerindex-web