Add SymLink helper and ignore duplicated files from this repository (maybe is there a better way ?)

.gitignore

 
 Assets/UnityHDRI.meta
 Assets/UnityHDRI/Gareoult/GareoultWhiteBalanced.exr
+Assets/GraphFramework/*
+Assets/NewUI/*
+Assets/UnityShaderEditor/*

_ExternalSymLink.sh

+cd Assets
+ln -s ../External/MaterialGraphProject/Assets/GraphFramework GraphFramework
+ln -s ../External/MaterialGraphProject/Assets/NewUI NewUI
+ln -s ../External/MaterialGraphProject/Assets/UnityShaderEditor UnityShaderEditor