UX: add usage info in the UI

[landure]

Please add a Usage panel, or a bottom line with the available actions (à la Zellij).

When first running Impala, the user is lost on what to do if he/she had not read the README.

In addition, adding the info to the command help would be nice.

[pythops]

@landure Would be great if you can try the PR and let me know what you think ? 🙏