FindCUDA: Improve deprecation guidance wording

Simplified the text regarding adding sources to be more general as there's also
target_sources().

Improved the wording for FindCUDAToolkit to be more explicit of its usecase and
avoid using "superseded" since the common usecase of FindCUDA was superseded by
the language support.

Wording suggestions incopropated from discussion on #22203.

Modules/FindCUDA.cmake

@@ -8,13 +8,13 @@ It is no longer necessary to use this module or call ``find_package(CUDA)``
 for compiling CUDA code. Instead, list ``CUDA`` among the languages named
 in the top-level call to the :command:`project` command, or call the
 :command:`enable_language` command with ``CUDA``.
-Then one can add CUDA (``.cu``) sources to programs directly
-in calls to :command:`add_library` and :command:`add_executable`.
+Then one can add CUDA (``.cu``) sources directly to targets similar to other
+languages.
 
 .. versionadded:: 3.17
-  To find and use the CUDA toolkit libraries the :module:`FindCUDAToolkit`
-  module has superseded this module.  It works whether or not the ``CUDA``
-  language is enabled.
+  To find and use the CUDA toolkit libraries manually, use the
+  :module:`FindCUDAToolkit` module instead.  It works regardless of the
+  ``CUDA`` language being enabled.
 
 Documentation of Deprecated Usage
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^