doc: Add command to build OpenXR targets on macOS

Signed-off-by: utzcoz <[email protected]>

Author: utzcoz

BUILDING.md

@@ -157,6 +157,15 @@ cmake -G "Xcode" ../..
 
 Finally, open the build/macos/OPENXR.xcodeproj in Xcode to build the samples.
 
+If you want to build with command, you can run following command to check
+available targets and built `ALL_BUILD` target as example:
+
+```shell
+# In build/macos directory
+xcodebuild -list -project OPENXR.xcodeproj/
+xcodebuild -scheme ALL_BUILD build
+```
+
 ### Android
 
 ```sh