diff --git a/README.md b/README.md
index 0726622c0..6145cc3b7 100755
--- a/README.md
+++ b/README.md
@@ -18,9 +18,15 @@ cd ErfanGSIs
 ### For setting up requirements
     bash setup.sh
 
+### MAC must set function to ~/.zshrc or ~/.bash_profile on the last
+    function realpath() {
+    [[ $1 = /* ]] && echo "$1" || echo "$PWD/${1#./}"
+    }
+
 ### Generating GSI from stock firmware URL
 Example: for making OxygenOS of oneplus 7 pro firmware, you can use this command
 ```
 ./url2GSI.sh https://oxygenos.oneplus.net/OnePlus7ProOxygen_21.O.07_OTA_007_all_1905120542_fc480574576b4843.zip OxygenOS
 ```
 check url2GSI.sh for more info
+