[Docs] Clarify node create help text about cluster reference

[losinggeneration]

What

An attempt to make it more clear that node create can be used for both k3d cluster names and external clusters by URL.

Why

When I first looked at k3d node create, I didn't realize the cluster argument was for more than a k3d created cluster. I tried a few things before I searched the issues and found #549 & the PR that fixed it, #734 It might save some users some time if this is more clear in the help & documentation. I initially thought of adding a new section it the guides for this, but I'm not sure how common the use-case is.

Implications

Since it's documentation only, it's unlikely to be a breaking changes. A potential caveat would be a tool inspecting & expecting exact strings from the help: k3d node create -h. Since that's typically a pretty naive implementation, it's unlikely to cause any real world issues.

[iwilltry42]

LGTM! Thanks for clarifying this :)

[iwilltry42]

Thanks for your contribution @losinggeneration :)

I initially thought of adding a new section it the guides for this, but I'm not sure how common the use-case is.

This would be very welcome, e.g. paired with an example on how to setup a "distributed" cluster 🤔