Use XDG_CONFIG_HOME for config instead of ~/.jjconfig

[colemickens]

Expected Behavior

I was writing a home-manager module for jj and noticed that, at least per the tutorial, it expects a config file dumped in $HOME instead of respecting XDG dirs.

Actual Behavior

It follows XDG specs to allow users to have config files isolated to, for example, $HOME/.config/.

[colemickens]

ref:

jj/lib/src/settings.rs

Lines 32 to 44 in 76974a9

	pub fn for_user() -> Result<Self, config::ConfigError> {
	let mut config = config::Config::new();
	if let Some(home_dir) = dirs::home_dir() {
	config.merge(
	config::File::from(home_dir.join(".jjconfig"))
	.required(false)
	.format(config::FileFormat::Toml),
	)?;
	}
	Ok(UserSettings { config })
	}

also, this looks like the most popular library: https://crates.io/crates/dirs