Add a community section at the bottom home page

I think HoloViz and hvPlot deserves a larger community. And we can help creating that by making it very clear where it is.

For example by adding a section to the bottom of the home page with a call to action **Join the Community**

With a tab for Questions(Discourse), Bug Reports (Github), Contributions (Github), Social with small .gif images that tell that these places are alive and kicking.