Adds some package docs (#479)

Was just browing godoc and noticed we are missing some docs that would
be quite useful.

manager/doc.go

@@ -0,0 +1,7 @@
+// Package manager provides access to kubernetes resources for providers.
+//
+// DEPRECATION WARNING:
+// Though this package is still in use, it should be considered deprecated as it
+// is just wrapping a k8s client and not much else.
+// Implementers should look at replacing their use of this with something else.
+package manager

vkubelet/api/doc.go

@@ -0,0 +1,3 @@
+// Package api implements HTTP handlers for handling requests that the kubelet
+// would normally implement, such as pod logs, exec, etc.
+package api

vkubelet/doc.go

@@ -0,0 +1,44 @@
+/*
+Package vkubelet implements the core virtual-kubelet framework.
+It contains everything reuired to implement a virtuak-kubelet, including the
+core controller which reconciles pod states and API endpoints for things like
+pod logs, exec, attach, etc.
+
+To get started, call the `New` with the appropriate config. When you are ready
+to start the controller, which registers the node and starts watching for pod
+changes, call `Run`. Taints can be used ensure the sceduler only schedules
+certain workloads to your virtual-kubelet.
+
+	vk := vkubelet.New(...)
+	// setup other things
+	...
+	vk.Run(ctx, ...)
+
+After calling start, cancelling the passed in context will shutdown the
+controller.
+
+Up to this point you have a running virtual kubelet controller, but no HTTP
+handlers to deal with requests forwarded from the API server for things like
+pod logs (e.g. user calls `kubectl logs myVKPod`).  This package provides some
+helpers for this: `AttachPodRoutes` and `AttachMetricsRoutes`.
+
+	mux := http.NewServeMux()
+	vkubelet.AttachPodRoutes(provider, mux)
+
+You must configure your own HTTP server, but these helpers will add handlers at
+the correct URI paths to your serve mux. You are not required to use go's
+built-in `*http.ServeMux`, but it does implement the `ServeMux` interface
+defined in this package which is used for these helpers.
+
+Note: The metrics routes may need to be attached to a different HTTP server,
+depending on your configuration.
+
+For more fine-grained control over the API, see the `vkubelet/api` package which
+only implements the HTTP handlers that you can use in whatever way you want.
+
+This uses open-cenesus to implement tracing (but no internal metrics yet) which
+is propagated through the context. This is passed on even to the providers. We
+may look at supporting custom propagaters for providers who would like to use a
+different tracing format.
+*/
+package vkubelet