Storybook: Add documentation for keyboard shortcuts

[ratkosolar]

Is your feature request related to a problem? Please describe
We use Storybook a lot in my team and sometimes we forget the keyboard shortcuts for toggling the sidemenu/addons panels. Last time we did, it took us 10mins googling to find a way to open the addons panel :D so it would be really handy if there was a page in docs that lists all of the keyboard shortcuts.

Describe the solution you'd like
Add a "Keyboard shortcuts" page in the documentation that will be very easy to find using the search box

Are you able to assist to bring the feature to reality?
yes, I can

[shilman]

I agree it's probably worth a mention, at least to say that you can find the keyboard shortcuts in the menu UI:

cc @jonniebigodes