Add return to top shortcuts to our documentations

[eugenepeh]

Currently all the shortcut links in our documentations are "one way trip". We should make it further user-friendly by adding return to top link at the end of each section.

[Zhiyuan-Amos]

@yamgent I will put this as an first timer issue, since the person can refer to my existing code and work on it :P

Whoever decides to work on this, refer to #496.

[C-likethis123]

Hello, I'm interested! Can I proceed to work on this issue?

[eugenepeh]

@C-likethis123 sure, go ahead