Update README.md (Added note for Win/OSX/WSL) (#11)

Author: SergeAgeyev

README.md

@@ -68,3 +68,10 @@ Adjust the cmake parameters dependent on your requirements.
 
 The generated [Class documentation](https://pschatzmann.github.io/Arduino-Emulator/html/annotated.html). 
 
+## Usage notes
+
+### Case-insensitive file systems (Windows, OSX, WSL)
+
+To avoid conflicts between system `string.h` and Arduino’s string library `String.h`, 
+just do not put `(include)/api` to include path. Put `(include)` and `(include)/api/deprecated` instead.
+This usual way to resolve this conflict in all Arduino cores.