Help: Add more documentation for CMAKE_<LANG>_SIMULATE_ID

Signed-off-by: Deniz Bahadir <[email protected]>

Help/variable/CMAKE_LANG_SIMULATE_ID.rst

@@ -1,9 +1,13 @@
 CMAKE_<LANG>_SIMULATE_ID
 ------------------------
 
-Identification string of "simulated" compiler.
+Identification string of the "simulated" compiler.
 
 Some compilers simulate other compilers to serve as drop-in
 replacements.  When CMake detects such a compiler it sets this
 variable to what would have been the :variable:`CMAKE_<LANG>_COMPILER_ID` for
 the simulated compiler.
+
+.. note::
+  In other words, this variable describes the ABI compatibility
+  of the generated code.