[Editorial] Add missing stable status markers (open-telemetry#682)

Author: trask

docs/runtime/jvm-metrics.md

@@ -188,6 +188,8 @@ of `[ 0.01, 0.1, 1, 10 ]`.
 
 ## JVM Threads
 
+**Status**: [Stable][DocumentStatus]
+
 **Description:** Java Virtual Machine (JVM) metrics captured under the namespace `jvm.thread.*`
 
 ### Metric: `jvm.thread.count`
@@ -228,6 +230,8 @@ Note that this is the number of platform threads (as opposed to virtual threads)
 
 ## JVM Classes
 
+**Status**: [Stable][DocumentStatus]
+
 **Description:** Java Virtual Machine (JVM) metrics captured under the namespace `jvm.class.*`
 
 ### Metric: `jvm.class.loaded`