How to install older versions of packages?
It may be documented somewhere, and it may be able to guess. But it should be stated at a more prominent place.

From  https://github.com/nim-lang/nimble we have for latest commit:

```
$ nimble install nimgame@#head
$ nimble install nimgame@"> 0.5"
```

gintro is tagged v0.6.0 for latest, version before was v0.5.5. How to get v0.5.5? My guesses

```
nimble install gintro@#=v0.5.5
nimble install gintro@#=0.5.5
nimble install gintro@#v0.5.5
nimble install gintro@#0.5.5
```

I assume at least one of these should work. Or no, maybe we have to remove the #
