clarify behavior of helm update

[krancour]

I learned today that when I helm update, it is only updating the charts in my cache. Charts in my workspace don't get refreshed. (I understand this is because the updates may conflict with local modifications.) So, on a subsequent helm install deis/deis, I was installing from stale charts.

I should have done this instead:

$ helm update
$ helm fetch deis/deis
$ helm install deis/deis

Again, I understand the reasoning behind not doing this. It is working exactly as designed, but it may still violate the principle of least surprise. Since the fetch from the cache was implicit in the initial helm install deis/deis, it was surprising that it would not have been in a subsequent installs. Also, because I had not made any local edits to the charts, I was only nominally aware of the workspace's existence. (I mean, I knew it was there, but wasn't thinking about it.) Knowing that local workspace needs to be explicitly refreshed (or even knowing it exists) is a detail a novice helm user can too easily overlook.

I don't pretend to know what the right answer to this is. Perhaps the workflow needs some tweaking. Alternatively, perhaps the workflow as it exists now just needs to be documented better.