Generate hotkeys section/doc using script and check with CI

[amanagr]

All the keybindings used by zulip-terminal are stored in zulipterminal/config.py. We can generate README section of the hotkeys by travic CI.

We can create a different section for hotkeys that are imported from urwid and urwid_readline libraries.

[punchagan]

There should be a tool that developers can run locally, to generate this section of the README. TravisCI should only check that any commit doesn't miss out on doing that, when keyconfig has changed in anyway. Some sort of a test can be run that compares the output of README when this script is run, and the README committed to the repo.

[neiljp]

I just thought this myself when opening #165 for some recent changes, and #164 for starred messages :)

[neiljp]

I believe we've discussed moving the hotkeys from README into docs/, so that might be a good first step, updating all the links, followed by the automatic synchronization via a script and then checking that with a GitHub Action (since we don't use Travis now).

[neiljp]

This is a similar issue to #892.