Try to add some more documentation to testables

Test: runtest --path frameworks/base/tests/testables/tests
Change-Id: I3dc39f05c3b91929a7d37b28879e31fb699f7334
diff --git a/tests/testables/src/android/testing/BaseFragmentTest.java b/tests/testables/src/android/testing/BaseFragmentTest.java
index 32ee091..5cedbdf 100644
--- a/tests/testables/src/android/testing/BaseFragmentTest.java
+++ b/tests/testables/src/android/testing/BaseFragmentTest.java
@@ -80,6 +80,10 @@
         });
     }
 
+    /**
+     * Allows tests to sub-class TestableContext if they want to provide any extended functionality
+     * or provide a {@link LeakCheck} to the TestableContext upon instantiation.
+     */
     protected TestableContext getContext() {
         return new TestableContext(InstrumentationRegistry.getContext());
     }