Add deprecation notice to README

Added deprecation notice and links to recent changes.

Author: jay7x

README.md

@@ -1,3 +1,14 @@
+# :warning: Deprecation notice
+
+Rsyslog project evolved significantly in last few years. See the changes related:
+1. [imhttp: expose stats via Prometheus endpoint](https://github.com/rsyslog/rsyslog/pull/5983) (released in v8.2510)
+2. [sidecar: add Prometheus impstats exporter sidecar](https://github.com/rsyslog/rsyslog/pull/6329) (released in v8.2602)
+3. [impstats: add VictoriaMetrics push support via Prometheus Remote Write](https://github.com/rsyslog/rsyslog/pull/6504) (released in v8.2602)
+
+Please use native rsyslog options now!
+
+Thank you for using this project!
+
 # rsyslog prometheus exporter
 
 This software acts like a syslog server and prometheus exporter at the same