Help: update policy 0078 documentation

Help/policy/CMP0078.rst

@@ -1,6 +1,8 @@
 CMP0078
 -------
 
+:module:`UseSWIG` generates standard target names.
+
 Starting with CMake 3.13, :module:`UseSWIG` generates now standard target
 names. This policy provides compatibility with projects that expect the legacy
 behavior.