Update README.md

Author: alexferl

README.md

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 # tinysyslog [![Go Report Card](https://goreportcard.com/badge/github.com/alexferl/tinysyslog)](https://goreportcard.com/report/github.com/alexferl/tinysyslog)
 
 A tiny and simple syslog server with log rotation. tinysyslog was born out of the need for a tiny, easy to set up and 
-use syslog server that simply writes every incoming log (RFC5424 format) to a file that is automatically rotated, 
+use syslog server that simply writes every incoming log (in [RFC 5424](https://datatracker.ietf.org/doc/html/rfc5424) format **only**) to a file that is automatically rotated, 
 to stdout or stderr (mostly for Docker) and or to Elasticsearch.
 tinysyslog is based on [go-syslog](https://github.com/mcuadros/go-syslog) and [lumberjack](https://github.com/natefinch/lumberjack).