[Documentation] Clarification of the completion key(s)?

- OS: Linux (Arch)
- Python: 3.7.4
- litecli: 1.1.0

This is a great tool (thanks!), but I was deterred from considering it by the references to completing with the "Right-arrow" key in the documentation (and UI). I'm used to completing with the standard GNU Readline Tab key (as in sqlite) and never use arrow keys for completion and don't use any tools which do by default (it's been a while since I last tried [fish](https://fishshell.com/docs/current/index.html#autosuggestions)).

I then came here (after looking through the documentation on the site) to see if there's any way to override this setting but couldn't find one, so I looked elsewhere. (Actually, I tried to install it anyway to see if I could live with the weird key, but [couldn't get it to install on Arch Linux](https://github.com/dbcli/litecli/issues/70).)

After getting frustrated with the default SQLite CLI again, I decided to give this another go and was delighted to find that tab-completion works as expected for keywords and identifiers, and that the arrow key is only used to complete **history** suggestions :+1:.

Now that I know this, the documentation makes perfect sense, but it might be worth tweaking it slightly to avoid giving the impression that the right-arrow key is required for all completions.