documentation of flags: avoid-version is not there

[hannesm]

Hey,

I tried to find documentation of the avoid-version flag - but was unable to find any (apart from a series of PR). It would be great to have this flag documented -- I think it is very useful, especially for release candidates etc. :)

Thanks a lot for your work and consideration,

Hannes

[dra27]

I've cheekily assigned the feature's author to add the docs 😉