Update release notes a bit

[skip ci]

doc/RELEASE-NOTES.md

@@ -28,6 +28,25 @@ Enhancements:
     now an `unrealircdctl.exe` that can be used to do similar things to what
     you can do on *NIX. Supported operations are: `rehash`, `reloadtls`,
     `mkpasswd`, `gencloak` and `spkifp`.
+* There is now an option to make [Spamfilter](https://www.unrealircd.org/docs/Spamfilter)
+  UTF8-aware. You need to `set { spamfilter { utf8-support yes; } }`
+  * Case insensitive matches work better. For example, with extended
+    Latin, a spamfilter on `ę` now also matches `Ę`.
+  * Other PCRE2 features such as [\p](https://www.pcre.org/current/doc/html/pcre2syntax.html#SEC5)
+    are now available. For example you can now set a spamfilter with the regex
+    `\p{Arabic}` to block all Arabic script, or `\p{Cyrillic}` to
+    block all Cyrillic script (such as Russian).
+    Please do use these new tools with care. Blocking an entire language
+    or script is quite a drastic measure.
+  * These new features require the PCRE2 10.36 regex library. Most people
+    will have a lower version of PCRE2 on the system, so then UnrealIRCd
+    will fallback to using the UnrealIRCd-shipped-library 10.39.
+    The downside to that is that compiling during `./Config` may take
+    a little longer than usual.
+  * If you try this new utf8-support for spamfilter, let us know if it works
+    well for you or not, so we can decide if we want to make this the
+    default in later versions. (In the past there were some issues with it
+    in the PCRE2 library, matching too much or too little)
 * New option [set::server-notice-show-event](https://www.unrealircd.org/docs/Set_block#set::server-notice-show-event)
   which can be set to `no` to hide the event information (eg `connect.LOCAL_CLIENT_CONNECT`)
   in server notices. This can be overriden per-oper in the