add description for caldav servers/clients categories

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

README.md

@@ -276,6 +276,8 @@ _See also: [Comparison of CalDAV and CardDAV implementations - Wikipedia](https:
 
 **[`^        back to top        ^`](#)**
 
+[CalDAV](https://en.wikipedia.org/wiki/CalDAV) and [CardDAV](https://en.wikipedia.org/wiki/CardDAV) protocol servers.
+
 - [Baïkal](https://sabre.io/baikal/) - Lightweight CalDAV and CardDAV server based on sabre/dav. ([Source Code](https://github.com/sabre-io/Baikal)) `GPL-3.0` `PHP`
 - [calypso](https://keithp.com/calypso/) - Python-based CalDAV and CardDAV server, forked from Radicale. ([Source Code](https://keithp.com/git/calypso.git)) `GPL-3.0` `Python`
 - [DAViCal](https://www.davical.org/) - Server for calendar sharing (CalDAV) that uses a PostgreSQL database as a data store. ([Source Code](https://gitlab.com/davical-project/davical)) `GPL-2.0` `PHP`
@@ -287,10 +289,12 @@ _See also: [Comparison of CalDAV and CardDAV implementations - Wikipedia](https:
 - [Xandikos](https://github.com/jelmer/xandikos) - Open source CardDAV and CalDAV server with minimal administrative overhead, backed by a Git repository. `GPL-3.0` `Python`
 
 
-### Calendar & Contacts - CalDAV or CardDAV Web-based Clients
+### Calendar & Contacts - CalDAV or CardDAV Web-based Clients.
 
 **[`^        back to top        ^`](#)**
 
+[CalDAV](https://en.wikipedia.org/wiki/CalDAV) and [CardDAV](https://en.wikipedia.org/wiki/CardDAV) protocol web clients/interfaces
+
 - [AgenDAV](https://agendav.github.io/agendav/) - Multilanguage CalDAV web client with a rich AJAX interface and shared calendars support. ([Source Code](https://github.com/agendav/agendav)) `GPL-3.0` `PHP`
 - [Bloben](https://bloben.com) - CalDAV web client. ([Demo](https://demo.bloben.com/api/v1/users/login-demo?username=demo&password=Bg8v16a4q7gvC&redirect=https://demo.bloben.com/calendar?demo=true), [Source Code](https://github.com/nibdo/bloben-app)) `AGPL-3.0` `Docker`
 - [EteSync Web](https://www.etesync.com/faq/#web-client) - EteSync's official Web-based client (i.e., their Web app). ([Demo](https://client.etesync.com/), [Source Code](https://github.com/etesync/etesync-web)) `AGPL-3.0` `Javascript`