DNS: clarify that the section is about DNS-based ad blockers (#3941)

- DNS servers or other management tools should be added to https://github.com/awesome-foss/awesome-sysadmin#dns---servers or https://github.com/awesome-foss/awesome-sysadmin#dns---control-panels--domain-management instead

README.md

@@ -750,14 +750,13 @@ _See also: [dbdb.io - Database of Databases](https://dbdb.io/)_
 
 **[`^        back to top        ^`](#awesome-selfhosted)**
 
-[DNS](https://en.wikipedia.org/wiki/Domain_Name_System) servers and management tools.
+[DNS](https://en.wikipedia.org/wiki/Domain_Name_System) servers and management tools with advertisement blocking funtionality, primarly aimed at home or small networks.
 
 _See also: [awesome-sysadmin/DNS - Servers](https://github.com/awesome-foss/awesome-sysadmin#dns---servers), [awesome-sysadmin/DNS - Control Panels & Domain Management](https://github.com/awesome-foss/awesome-sysadmin#dns---control-panels--domain-management)_
 
 - [blocky](https://github.com/0xERR0R/blocky) - Fast and lightweight DNS proxy (like Pi-hole) as ad-blocker for local network with many features. `Apache-2.0` `Go`
 - [Maza ad blocking](https://maza-ad-blocking.andros.dev/) - Local ad blocker. Like Pi-hole but local and using your operating system. ([Source Code](https://github.com/tanrax/maza-ad-blocking)) `Apache-2.0` `Bash`
-- [SmartDNS](https://github.com/pymumu/smartdns) - A local DNS server to obtain the fastest website IP for the best Internet experience, supports DoT, DoH. `GPL-3.0` `C`
-- [Technitium DNS Server](https://technitium.com/dns/) - An open source authoritative as well as recursive DNS server that can be used for self hosting a DNS server for privacy & security. ([Source Code](https://github.com/TechnitiumSoftware/DnsServer)) `GPL-3.0` `Docker/C#`
+- [Technitium DNS Server](https://technitium.com/dns/) - Authoritative/recursive DNS server with ad blocking functionality. ([Source Code](https://github.com/TechnitiumSoftware/DnsServer)) `GPL-3.0` `Docker/C#`
 
 
 ### Document Management