Update README.md

Co-authored-by: Christian Lück <[email protected]>

Author: yadaiio

README.md

@@ -15,7 +15,7 @@ This library implements SSDP as defined in the
 and uses HTTP over Multicast UDP (HTTPMU) as defined in the
 [IETF draft](https://tools.ietf.org/html/draft-goland-http-udp-01).
 As an alternative, some devices use DNS-Based Service Discovery (DNS-SD) instead
-as defined in [RFC 6763](https://tools.ietf.org/html/rfc6763).
+as defined in [RFC 6763](https://www.rfc-editor.org/rfc/rfc6763.html).
 
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