Disambiguate URL usage in main binary CLI help message

[marcospb19]

Addresses #11199's confusion.

Release Notes:

• N/A

[marcospb19]

Well, I thought this wasn't supposed to support relative files without the file:// prefix, cause it's not working for me, but when I look at the code, it looks like it should:

zed/crates/zed/src/main.rs

Lines 1021 to 1036 in 10792ee

	fn parse_url_arg(arg: &str, cx: &App) -> Result<String> {
	match std::fs::canonicalize(Path::new(&arg)) {
	Ok(path) => Ok(format!("file://{}", path.display())),
	Err(error) => {
	if arg.starts_with("file://")
	|| arg.starts_with("zed-cli://")
	|| arg.starts_with("ssh://")
	|| parse_zed_link(arg, cx).is_some()
	{
	Ok(arg.into())
	} else {
	Err(anyhow!("error parsing path argument: {}", error))
	}
	}
	}
	}

Now I'm confused if this not opening relative paths for me is intended or a bug... I need to take another look.