add back harness environment author description

Author: mmalerba

src/cdk/testing/testing.md

@@ -549,9 +549,10 @@ may need to explicitly wait for tasks outside `NgZone`, as this does not happen
 
 ### API for harness environment authors
 
-Out-of-the-box, Angular CDK's component harnesses can be used in Protractor E2E tests and Karma unit
-tests. Developers can support additional environments by creating custom implementations of
-`TestElement` and `HarnessEnvironment`. 
+Harness environment authors are developers who want to add support for using component harnesses in
+additional testing environments. Out-of-the-box, Angular CDK's component harnesses can be used in
+Protractor E2E tests and Karma unit tests. Developers can support additional environments by
+creating custom implementations of `TestElement` and `HarnessEnvironment`. 
 
 #### Creating a `TestElement` implementation for the environment