Incorrect reference to non-existent `linkerd-base` chart in docs

[Adam Gardner]

In the docs for automatically rotating control-plane tls credentials, in the section on installing with Helm, the following statement is written:

Installing with Helm
For installing with Helm, first install the linkerd-crds and linkerd-base charts:

helm install linkerd-base -n linkerd linkerd/linkerd-crds
helm install linkerd-base -n linkerd --create-namespace linkerd/linkerd-base

There's three problems here: first, the first command uses the linkerd namespace before the second command creates it; second, the linkerd-base chart doesn't actually seem to exist; and third, even if it did, this is instructing the user to install two different charts into the same namespace under the same release name (which is impossible).

As I understand it, the chart that is now called linkerd-crds was at one time going to be called linkerd-base, and someone got a bit muddled when updating the docs.