Add changelog note

Author: crobert-1

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### 🛑 Breaking changes 🛑
+
+- (Splunk) Support for Oracle Linux 7 has been dropped ([#](https://github.com/signalfx/splunk-otel-collector/pull/))
+
 ## v0.120.0
 
 This Splunk OpenTelemetry Collector release includes changes from the [opentelemetry-collector v0.120.0](https://github.com/open-telemetry/opentelemetry-collector/releases/tag/v0.120.0) and the [opentelemetry-collector-contrib v0.120.1](https://github.com/open-telemetry/opentelemetry-collector-contrib/releases/tag/v0.120.1) releases where appropriate.