add referene to the spec for otpauth urls (which is still a draft)

src/main.zig

@@ -195,6 +195,7 @@ fn parseArgs(allocator: Allocator, args: []const []const u8) !Args {
     return result;
 }
 
+// see https://www.ietf.org/archive/id/draft-linuxgemini-otpauth-uri-01.txt
 fn parseOtpAuthUrl(allocator: Allocator, url: []const u8) !OtpAuthUrl {
     const uri = try std.Uri.parse(url);