[Docs] Add documentation for the hot keys feature

[miroiu]

There's no documentation about the hot keys displayed for pending connections. We should document the following topics:

• customizing the display mode
• limiting the maximum number of hot keys
• customizing the hot key visual

The feature was implemented here: #227

[sailanka02]

Hi Miroio, I am a new contributor and would like to know if I can be assigned this task if it's not done yet.

[miroiu]

Hi, you can have it.