Help: for command enable_testing, explain relation to module CTest.

Help/command/add_test.rst

@@ -55,7 +55,8 @@ file produced by target ``myexe``.
 
   CMake will generate tests only if the :command:`enable_testing`
   command has been invoked.  The :module:`CTest` module invokes the
-  command automatically when the ``BUILD_TESTING`` option is ``ON``.
+  command automatically unless the ``BUILD_TESTING`` option is turned
+  ``OFF``.
 
 ---------------------------------------------------------------------
 

Help/command/enable_testing.rst

@@ -7,7 +7,14 @@ Enable testing for current directory and below.
 
   enable_testing()
 
-Enables testing for this directory and below.  See also the
-:command:`add_test` command.  Note that ctest expects to find a test file
-in the build directory root.  Therefore, this command should be in the
-source directory root.
+Enables testing for this directory and below.
+
+This command should be in the source directory root
+because ctest expects to find a test file in the build
+directory root.
+
+This command is automatically invoked when the :module:`CTest`
+module is included, except if the ``BUILD_TESTING`` option is
+turned off.
+
+See also the :command:`add_test` command.