This adds a hidden 'helm doc' command that generates documentation out
of the Helm help text.
Currently it can create:
- man pages for HELM(1)
- Markdown documentation
- bash autocompletions
Those are the three built-ins for Cobra.
The command is hidden so that it doesn't show up to the regular user,
since this is really a specialized task. It has the advantage of making
it trivially easy to install man pages and bash completion at installation time.
