Add explanatory comments to action.List and action.History

While the comments may seem to state the obvious to someone with helm CLI
experience, an SDK-first user may find these comments helpful.

Signed-off-by: Daniel Lipovetsky <dlipovetsky@d2iq.com>

pkg/action/history.go

@@ -26,6 +26,9 @@ import (
 // History is the action for checking the release's ledger.
 //
 // It provides the implementation of 'helm history'.
+// It returns all the revisions for a specific release.
+// To list up to one revision of every release in one specific, or in all,
+// namespaces, see the List action.
 type History struct {
 	cfg *Configuration
 

pkg/action/list.go

@@ -98,6 +98,9 @@ const (
 // List is the action for listing releases.
 //
 // It provides, for example, the implementation of 'helm list'.
+// It returns no more than one revision of every release in one specific, or in
+// all, namespaces.
+// To list all the revisions of a specific release, see the History action.
 type List struct {
 	cfg *Configuration