Add GitHub bottons

[rsokl]

We need more stars!!

https://buttons.github.io/

And maybe we can add an issue button to each page?

[alexander-ding]

Maybe a Star button on the top of the homepage?
For the issue button, maybe something wrapped in <div class="alert alert-info"></div> at the end of each page?

[rsokl]

@alexander-ding it looks like modifying the header/footer the RTD theme is a bit complicated. Although I was able to hijack their template to replace "View Page Source" with "Star on GitHub" (#168 )