cli: `-C` alias for `--conditions` flag

Use cases like --conditions=development should be easy to type, so having an alias allows for a much easier node -C=development app.js command and makes this workflow feel more natural, especially since we haven't otherwise given precedence to development / production modes.

-c and -e are both already taken so -C is used instead, per discussion below.

I've also added an example and reference to the CLI documentation.

@nodejs/modules