Document piping to `turso db shell`

[penberg]

You can pipe SQL commands to the shell with:

echo "SELECT 1;" | turso db shell endless-odin

Let's document that for discoverability.

[CodingDoug]

The fact that you can do this doesn't really mean that someone should do this. The problem right now is that the handling of input and output is a bit of a mess right now from the perspective of someone trying to send SQL non-interactively via stdin. What the CLI needs to do is:

• Detect when it's invoked non-interactively (not having a TTY)
• Suppress all normal output (welcome message, prompts, tabular output)
• Define what the output should be given that input could be anything (maybe a parseable summary of what happened in total?)
• Define what happens in the event of a SQL error (stop? keep processing input?)
• Define useful exit codes