Add `description` to ColorArgument.
Add `description` to ColorArgument.

Commandant output looks nicer:
```
[--color ‘auto’ || ‘always’ || ‘never’]
Terminal coloring and styling
```

erichoracek/Carthage,abbeycode/Carthage,erichoracek/Carthage,NachoSoto/Carthage,abbeycode/Carthage,flovilmart/Carthage,NachoSoto/Carthage,abbeycode/Carthage,erichoracek/Carthage,flovilmart/Carthage,abbeycode/Carthage,NachoSoto/Carthage,erichoracek/Carthage,flovilmart/Carthage