Update cmd description

[rikhuijzer]

I don't see a reason in the action.yml why version is mandatory to use cmd.

[DilumAluthge]

Suppose that the user adds a cmd of the form CompatHelper.main(; foo = ...). Since the user has not specified the version, it will use the default version = '3'.

Now suppose that I release CompatHelper 4.0.0, which removed the foo kwarg, which is perfectly fine to do in a major release.

Now, here's the tricky part. I want to be able to easily upgrade the Julia ecosystem to CompatHelper v4, so I edit the action.yml file in this repo to change the default from version = '3' to version = '4'. But, I don't want everyone to have to edit their CompatHelper.yml files, so I make this change in the v1 tag of this repo.

But now the action is broken for the user that was doing a custom cmd.

So most users don't need to set version. But if a user sets cmd, they must set version to prevent the action from suddenly breaking.

[rikhuijzer]

You're right