Add warning note for macos

Author: JadedBlueEyes

README.md

@@ -2,7 +2,10 @@
 
 [![Chat on Matrix](https://img.shields.io/badge/chat%20on-matrix-white?logo=matrix)](https://matrix.to/#/#fendapp:ellis.link)
 
-FendApp is a calculator for unit-aware calculations across a wide range of domains. It offers various features, including the ability to effortlessly convert between hundreds of built-in units. 
+FendApp is a calculator for unit-aware calculations across a wide range of domains. It offers various features, including the ability to effortlessly convert between hundreds of built-in units.
+
+> [!note] MacOS: 'app is damaged and can't be opened'
+> If you're on macOS, please note that macOS may say the app is damaged and can't be opened. If that is the case, you will need to use the `xattr -cr <file>` command to tell macOS the app is safe. A tutorial for this can be found [here](https://www.youtube.com/watch?v=xjCMBisZ4Is).
 
 ![Screenshot of FendApp calculating the £/hour from total pay and total hours, and converting it into $/hour](https://github.com/user-attachments/assets/5cd9b993-1a75-4c6d-9e58-87736f52a69f)