Add translatable string for config parse error

Signed-off-by: AnErrupTion <anerruption@disroot.org>

src/config/Lang.zig

@@ -6,6 +6,7 @@ err_alloc: []const u8 = "failed memory allocation",
 err_bounds: []const u8 = "out-of-bounds index",
 err_brightness_change: []const u8 = "failed to change brightness",
 err_chdir: []const u8 = "failed to open home folder",
+err_config: []const u8 = "unable to parse config file",
 err_console_dev: []const u8 = "failed to access console",
 err_dgn_oob: []const u8 = "log message",
 err_domain: []const u8 = "invalid domain",