Help: Demonstrate using set_target_properties with CUDA architectures

A common anti-pattern is to copy from the `CUDA_ARCHITECTURES` documentation.
If at any point the user tries to simplify by changin `set_property` to `set_target_properties` the code breaks.

To better train users, provide and example of how to set multiple
CUDA architectures with `set_target_properties`.

Help/policy/CMP0104.rst

@@ -41,7 +41,7 @@ Examples
 
 .. code-block:: cmake
 
-  set_property(TARGET tgt PROPERTY CUDA_ARCHITECTURES 35 50 72)
+  set_target_properties(tgt PROPERTIES CUDA_ARCHITECTURES "35;50;72")
 
 Generates code for real and virtual architectures ``30``, ``50`` and ``72``.
 

Help/prop_tgt/CUDA_ARCHITECTURES.rst

@@ -25,7 +25,7 @@ Examples
 
 .. code-block:: cmake
 
-  set_property(TARGET tgt PROPERTY CUDA_ARCHITECTURES 35 50 72)
+  set_target_properties(tgt PROPERTIES CUDA_ARCHITECTURES "35;50;72")
 
 Generates code for real and virtual architectures ``30``, ``50`` and ``72``.