ref(docs): import docs into v3.helm.sh

This is a significant development change to the documentation. Essentially, this moves the content of the docs/ dir in helm/helm over to helm-www similar to kubernetes/kubernetes and kubernetes/website.

This provides several significant enhancements over the existing system:

1. No more URL redirect munging in gulpfile.js
2. No requirements on cloning helm/helm to build the site
3. No need to open multiple PRs when introducing new documentation material (one for the docs, and one to add to the menus).

Signed-off-by: Matthew Fisher <matt.fisher@microsoft.com>

.gitignore

@@ -15,6 +15,5 @@ app/*
 source/
 source/*
 static/*
-content/docs/*
 helm.sh/
-docs.helm.sh/
+docs.helm.sh/