kike: add a comment about identifier encoding

kike.c

@@ -233,6 +233,13 @@ irc_is_valid_host (const char *host)
 		|| irc_is_valid_hostaddr (host);
 }
 
+// TODO: currently, we are almost encoding-agnostic (strings just need to be
+// ASCII-compatible).  We should at least have an option to enforce a specific
+// encoding, such as UTF-8.  Note that with Unicode we should not allow all
+// character clasess and exclude the likes of \pM with the goal of enforcing
+// NFC-normalized identifiers--utf8proc is a good candidate library to handle
+// the categorization and validation.
+
 static bool
 irc_is_valid_user (const char *user)
 {