Documentation on pre-release

[bluebrown]

Is your feature request related to a problem? Please describe.

I am trying to use the pre-release feature, but I cannot figure out how this is supposed to work. I have 2 problems here.

1. I am not able to increment the pre-release version number suffix. i.e. beta.1 to beta.2
2. I am not able to get the current pre-release version. i.e. v0.1.0-beta.1

Describe the solution you'd like

It would be good if it was documented here https://convco.github.io/version/

[bluebrown]

Ok nevermind. The problem was I had already a release version. i.e. 0.1.2 and then the pre release options would create 0.1.2-beta.1 und further commands would prefer 0.1.2 over 0.1.2-beta.1.

Maybe this should bail out if someone tries to create a pre release for an already released version?