Help: Document Ninja generator conditional Fortran support

Closes: #14215

Help/generator/Ninja.rst

@@ -21,3 +21,13 @@ are generated:
 
 ``sub/dir/package``
   Runs the package step in the subdirectory, if any.
+
+Fortran Support
+^^^^^^^^^^^^^^^
+
+The ``Ninja`` generator conditionally supports Fortran when the ``ninja``
+tool has the required features.  As of this version of CMake the needed
+features have not been integrated into upstream Ninja.  Kitware maintains
+a branch of Ninja with the required features on `github.com/Kitware/ninja`_.
+
+.. _`github.com/Kitware/ninja`: https://github.com/Kitware/ninja/tree/features-for-fortran#readme

Help/release/dev/ninja-fortran.rst

@@ -0,0 +1,6 @@
+ninja-fortran
+-------------
+
+* The :generator:`Ninja` generator learned to conditionally support
+  Fortran when using a ``ninja`` tool that has the necessary features.
+  See generator documentation for details.