adding instructions on build & run on macOS Big Sur in readme

README.md

@@ -11,6 +11,17 @@ I intend to add more documentation and clarify some of the code and assets over
   - Make sure you have SDL2 headers & libraries, and make sure CMake can find them
   - All the art was made in [Aseprite](https://www.aseprite.org/). To modify or add new sprites, you'll need to use aseprite.
 
+### building on macOS Big Sur
+  - preinstall latest Xcode and the command line tools
+  - brew install cmake        // make sure CMake is 3.12+
+  - brew install sdl2         // make sure sdl2 is 2.0.12+
+  - git clone https://github.com/NoelFB/tiny_link.git 
+  - cd tiny_link
+  - git submodule init
+  - git submodule update
+  - cmake -G Xcode .
+  - open Xcode project file, select 'game' target, build and run on Xcode
+
 ![Screenshot](https://github.com/noelfb/tiny_link/raw/main/screenshot.png "Screenshot")
 
 ### box art