Clarify valid version range specifications

[jabbrwcky]

The help of helm states that you can specify a version range for a Helm chart:

--version string               specify a version constraint for the chart version to use. This constraint can be a specific tag (e.g. 1.1.1) or it may reference a valid range (e.g. ^2.0.0). If this is not specified, the latest version is used

But there is no documentation whatsoever what form of version constraints Helm accepts.

After some ddgo'ing I found that the used semver library https://github.com/Masterminds/semver has details in its README.

I think that at the very minimum the documentation should link to explain valid version ranges, better have a short paragraph replicating some examples.