Adds sdkman conf file and usage instructions (#499)

* Adds sdkman conf file and usage instructions

* Update README.md

Co-authored-by: Austin Lai <76412946+alai97@users.noreply.github.com>

---------

Co-authored-by: Austin Lai <76412946+alai97@users.noreply.github.com>

.sdkmanrc

@@ -0,0 +1,8 @@
+# Enable auto-env through the sdkman_auto_env config
+# Add key=value pairs of SDKs to use below
+#
+# Java version currently tracking what is present in -jmx agent builds
+# Agent is currently installing 'openjdk-11-jre-headless' from debian
+# See https://github.com/DataDog/datadog-agent/blob/3b6f07cb7d097837a7b9247c6119ead3309116ab/Dockerfiles/agent/Dockerfile#L136
+# and https://packages.debian.org/sid/openjdk-11-jre-headless
+java=11.0.21-amzn

README.md

@@ -61,6 +61,13 @@ JMXFetch uses [Lombok](https://projectlombok.org/) to modify classes and generat
 You may need to [enable annotation processors](https://projectlombok.org/setup/overview) to compile in your IDE.
 
 ## Useful Developer Settings
+
+### JDK version management
+[`sdkman`](https://sdkman.io/install) is recommended to manage multiple versions of Java.
+If you are an sdkman user, there is a config file present in this project with
+the recommended JDK version for development, use `sdk env` to activate it.
+
+
 ### Enabling file line numbers in log messages
 If you set the system property `-Djmxfetch.filelinelogging=true`, this will enable all log output to
 include the line number which emitted a given log.