Add comment in this file so it is in the generated file

src/characters/CharacterWidth.src.cpp

@@ -22,6 +22,10 @@
 // «gen-file-warning»
 //
 // CharacterWidth.cpp file is automatically generated - do not edit it.
+//
+// To build uni2characterwidth binary, add
+// -DKONSOLE_BUILD_UNI2CHARACTERWIDTH=TRUE to cmake-options
+//
 // To change anything here, edit CharacterWidth.src.cpp and regenerate the file
 // using following command:
 //