Add comments to explain how to configure OpenCV in the opencv_macos.B…

…UILD file.

PiperOrigin-RevId: 691204643

third_party/opencv_macos.BUILD

@@ -7,8 +7,29 @@ licenses(["notice"])  # BSD license
 
 exports_files(["LICENSE"])
 
-# The path to OpenCV is a combination of the path set for "macos_opencv"
-# in the WORKSPACE file and the prefix here.
+# Example configurations:
+#
+# To configure OpenCV 3, obtain the path of OpenCV 3 from Homebrew:
+#
+# $ brew ls opencv@3 | grep version.hpp
+# $ /opt/homebrew/Cellar/opencv@3/3.4.16_10/include/opencv2/core/version.hpp
+#
+# Then set path in "macos_opencv" rule in the WORKSPACE file to
+# "/opt/homebrew/Cellar" and the PREFIX below to "opencv@3/3.4.16_10".
+#
+#
+# To configure OpenCV 4, obtain the path of OpenCV 4 from Homebrew:
+#
+# $ brew ls opencv | grep version.hpp
+# $ /opt/homebrew/Cellar/opencv/4.10.0_12/include/opencv4/opencv2/core/version.hpp
+# $ /opt/homebrew/Cellar/opencv/4.10.0_12/include/opencv4/opencv2/dnn/version.hpp
+#
+# Then set path in "macos_opencv" rule in the WORKSPACE file to
+# "/opt/homebrew/Cellar" and the PREFIX below to "opencv/4.10.0_12". For OpenCV
+# 4, you will also need to adjust the include paths. The header search path
+# should be "include/opencv4/opencv2/**/*.h*" and the include prefix needs to
+# be set to "include/opencv4".
+
 PREFIX = "opt/opencv@3"
 
 cc_library(