add documentation generation flag to documentation

docs/Install.rst

@@ -58,6 +58,8 @@ Compile time features
 ``-DCM_ALL_TESTS_INTEGRATION=ON`` (default: ``OFF``)
   Enables integration/feature tests. Requires ``CM_ALL_TESTS`` to be
   enabled as well.
+``-DCM_ALL_AUTO_DOC=ON`` (default: ``OFF``)
+  Generate documentation using doxygen and Sphinx.
 ``-DCMAKE_BUILD_TYPE=Debug`` (default: ``Release``)
   Enable library internal debugging features. Using ``DebugWithOpt`` also
   turns on some optimizations.