Document the usage of the NodeFeature CRD API. Also re-organize the
documentation a bit, moving the description of NodeFeatureRule
controller from customization guide to nfd-master usage page.
Add a separate page for describing the custom resources used by NFD.
Simplify the Introduction page by moving the details of
NodeResourceTopology from there. Similarly, drop long
NodeResourceTopology example from the quick-start page, making the page
shorter and simpler.
