Better documentation for MeterGroup

[3tilley]

Hello,

I think the documentation could be improved for MeterGroup, for example there are no examples of how to create an array to pass into :value and there is no discussion of what MeterItem is. It looks like this was discussed in PrimeNG here.

In addition, it's been suggested here that if someone needs multiple items on a ProgressBar they should instead employ MeterGroup. However they are quite different, and in particular MeterGroup doesn't offer any indication of interactivity - is there a way to make it clear that it's a type that is updating similar to how ProgressBar makes that quite obvious? If there was a demonstration of using MeterGroup as a multi-item progress bar that would be amazing!