Add readme for v2 release.

Author: zzhlogin

README.md

@@ -13,6 +13,11 @@ can be exported in a variety of formats. In addition, the agent and exporter can
 command line arguments or environment variables. The net result is the ability to gather telemetry
 data from a Java application without any code changes.
 
+Note: There are 2.x releases and 1.x releases. The 2.0 release included significant breaking changes from [OpenTelemetry Agent for Java](https://github.com/open-telemetry/opentelemetry-java-instrumentation), 
+the details of which can be found in the [release notes](https://github.com/open-telemetry/opentelemetry-java-instrumentation/releases). 
+It is recommended to use the latest 2.x release which will have the latest features and improvements. 
+1.x will receive security patches for a limited time and will not include other bug fixes and enhancements.
+
 ## Getting Started
 
 Check out the [getting started documentation](https://aws-otel.github.io/docs/getting-started/java-sdk/auto-instr).

appsignals-tests/contract-tests/src/test/java/software/amazon/opentelemetry/appsignals/test/base/JMXMetricsContractTestBase.java

@@ -62,9 +62,10 @@ protected long getThreshold(String metricName) {
     switch (metricName) {
         // If maximum memory size is undefined, then value is -1
         // https://docs.oracle.com/en/java/javase/17/docs/api/java.management/java/lang/management/MemoryUsage.html#getMax()
-        // TODO: Figure out why tomcat thread counts can be negative.
+        // Thread count can be negative when excutor is null
+        // https://github.com/apache/tomcat/blob/1afe41491f0e56ec0a776db5ff84607f87ce6640/java/org/apache/tomcat/util/net/AbstractEndpoint.java#L1204
       case JMXMetricsConstants.TOMCAT_THREADS:
-        threshold = -3;
+        threshold = -2;
         break;
       case JMXMetricsConstants.JVM_HEAP_MAX:
       case JMXMetricsConstants.JVM_NON_HEAP_MAX: