Document cdbg_extra_class_path parameter to configure exploded WAR classpath explicitly.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=152151510

Author: emrekultursay

README.md

@@ -95,10 +95,10 @@ Google Compute Engine or on a virtual machine that does not allow API access to
 all Google Cloud services. This would require setting up a
 [service account](#service-account).
 
-### Web Servers
+### Application Servers
 
-Java web servers usually start through a bootstrap process, and each web server
-has its own way of customizing Java options.
+Java application servers usually start through a bootstrap process, and each
+application server has its own way of customizing Java options.
 
 #### Tomcat
 
@@ -123,6 +123,29 @@ Add `cdbg.ini` file to `/var/lib/jetty/start.d`:
 -agentpath:/opt/cdbg/cdbg_java_agent.so
 ```
 
+### Configuring Extra Classpath
+The agent needs to be able to find your application classes when it's running
+in an application server like Tomcat or Jetty. By default, the agent looks for
+the exploded root war directory. In other words, if you deployed a `ROOT.war`
+in Tomcat, the agent can find it without additional configuration.
+
+However, if you deployed your WAR file with a different name (e.g.,
+`myapp.war`), or that the exploded WAR directory is not under the default
+exploded root war directory (e.g., your exploded war is under
+`/opt/tomcat/webapps/myapp`), then you must
+let the agent know the full path to your application's classes using the
+`cdbg_extra_class_path` parameter.
+
+```none
+-agentpath:/opt/cdbg/cdbg_java_agent.so=--cdbg_extra_class_path=/opt/tomcat/webapps/myapp/WEB-INF/classes
+```
+
+You can specify multiple paths by using a "`:`" (colon) as the path delimiter.
+
+```none
+-agentpath:/opt/cdbg/cdbg_java_agent.so=--cdbg_extra_class_path=/opt/tomcat/webapps/myapp/WEB-INF/classes:/another/path/with/classes
+```
+
 ### Naming and Versioning
 
 Developers can run multiple applications and versions at the same time within