Help: Insert section headers in CPack module

The one extant section header was confusing at least:
Not all the doc page is on Variables.

Modules/CPack.cmake

@@ -7,8 +7,8 @@ CPack
 
 Build binary and source package installers.
 
-Variables common to all CPack generators
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Introduction
+^^^^^^^^^^^^
 
 The CPack module generates binary and source installers in a variety of
 formats using the cpack program.  Inclusion of the CPack module adds
@@ -23,6 +23,9 @@ installers on macOS and Windows), CPack generates installers that
 allow users to select individual application components to install.
 See :module:`CPackComponent` module for further details.
 
+CPack generators
+^^^^^^^^^^^^^^^^
+
 The :variable:`CPACK_GENERATOR` variable has different meanings in different
 contexts.  In a ``CMakeLists.txt`` file, :variable:`CPACK_GENERATOR` is a
 *list of generators*: and when :manual:`cpack <cpack(1)>` is run with no other
@@ -57,6 +60,9 @@ This is the key: For each generator listed in :variable:`CPACK_GENERATOR` in
 internally to *the one currently being used* and then include the
 :variable:`CPACK_PROJECT_CONFIG_FILE`.
 
+Variables common to all CPack generators
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
 Before including this CPack module in your ``CMakeLists.txt`` file, there
 are a variety of variables that can be set to customize the resulting
 installers.  The most commonly-used variables are: