Adding a reference to runtime metrics (#7407)

As suggested by @tylerbenson, adding a reference to the runtime metrics
reported by the agent.

instrumentation/jmx-metrics/javaagent/README.md

@@ -12,7 +12,9 @@ To control the time interval between MBean detection attempts, one can use the `
 
 ## Predefined metrics
 
-JMX Metric Insight comes with a number of predefined configurations containing curated sets of JMX metrics for popular application servers or frameworks. To enable collection for the predefined metrics, specify a list of targets as the value for the `otel.jmx.target.system` property. For example
+JMX is a popular metrics technology used throughout the JVM (see [runtime metrics](../../runtime-metrics/library/README.md)), application servers, third-party libraries, and applications.
+JMX Metric Insight comes with a number of predefined configurations containing curated sets of JMX metrics for frequently used application servers or frameworks.
+To enable collection of the predefined metrics, specify a list of targets as the value for the `otel.jmx.target.system` property. For example
 
 ```bash
 $ java -javaagent:path/to/opentelemetry-javaagent.jar \