add descriptions for xmpp servers/clients

- https://github.com/awesome-selfhosted/awesome-selfhosted/issues/2984

README.md

@@ -602,6 +602,8 @@ _Related: [Conference Management](#conference-management)_
 
 **[`^        back to top        ^`](#)**
 
+XMPP servers.
+
 - [ejabberd](https://www.ejabberd.im/) - XMPP instant messaging server. ([Source Code](https://github.com/processone/ejabberd)) `GPL-2.0` `Erlang`
 - [jackal](https://github.com/ortuman/jackal) - XMPP server with focus on stability, simple configuration and low resource consumption. `Apache-2.0` `Go`
 - [Kontalk](https://www.kontalk.org) - Kontalk is an Open Source Messenger, similar to WhatsApp (app for android only currently), including end-to-end encryption, server is based on Tigase XMPP Server. ([Source Code](https://github.com/kontalk)) `GPL-3.0` `Java`
@@ -617,6 +619,8 @@ _Related: [Conference Management](#conference-management)_
 
 **[`^        back to top        ^`](#)**
 
+XMPP Web clients/interfaces.
+
 - [Candy](https://candy-chat.github.io/candy/) - Multi user XMPP client written in Javascript. ([Source Code](https://github.com/candy-chat/candy)) `MIT` `Javascript`
 - [Converse.js](https://conversejs.org/) - Free and open-source XMPP chat client in your browser. ([Source Code](https://github.com/conversejs/converse.js)) `MPL-2.0` `Javascript`
 - [JSXC](https://jsxc.org) - Real-time XMPP web chat application with video calls, file transfer and encrypted communication. There are also versions for Nextcloud/Owncloud and SOGo. ([Source Code](https://github.com/jsxc/jsxc)) `MIT` `Javascript`