Added *COMBINED minimum requirement to readme

Author: Alexander Widerberg

README.md

@@ -62,7 +62,7 @@ cmake --build . --config Release
 cmake --install . --config Release
 ```
 
-**_NOTE_: The COMBINED options _ONLY_ work with the Xcode generator (-G Xcode)**
+**_NOTE_: The COMBINED options _ONLY_ work with the Xcode generator (-G Xcode) on CMake versions 3.14+!**
 
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