This patch adds a post-delete hook to the Helm chart that runs
"nfd-master --prune" in the cluster. This cleans up the node of labels,
annotations, taints and extended resources that were created by NFD.
Introduce two main sections "Deployment" and "Usage" and move "Developer
guide" to the top level, too. In particular, split the huge
deployment-and-usage file into multiple parts under the new main
sections. Move customization guide from "Advanced" to "Usage".
This patch also renames "Advanced" to "Reference" as only that is left
there is reference documentation.
