Added some documentation for homebrew crossinstallation scripts (#4)

README.md

@@ -3,3 +3,46 @@
 ## Tebako portability tools ##
 
 This repository contains cmake, shell scripts and include files aimed to support tebako builds on different platforms.
+
+## Homebrew cross-installation scripts ##
+
+Sometimes you need to build MacOS application in a foreign environment. For example, GitHub Actions provides x86 runners only, but you may need to build and package arm64 binary.
+Most of the applications rely on external dependencies, so on MacOS you will require a method to use another instance of homebrew to support the target environment.
+
+Among other tools this repository provides a set of simple scripts to cross install homebrew dependencies
+
+### arm64 packages on x86_64 system
+
+```
+    arm-brew-install <arm brew parent folder>
+    arm-brew-setup <arm brew folder> <formula to install 1> ... <formula to install 1>
+```
+
+For example
+
+```
+    arm-brew-install ~/test
+    arm-brew-setup ~/test glog gflags
+```
+
+Will create arm brew environment in ~/test/arm-homebrew and install glog and gflags formulae there
+
+
+### x86_64 packages on arm system
+
+```
+    x86_64-brew-install <x86_64 brew parent folder>
+    x86_64-brew-setup <x86_64 brew folder> <formula to install 1> ... <formula to install 1>
+```
+
+For example
+
+```
+    x86_64-brew-install ~/test
+    x86_64-brew-setup ~/test glog gflags
+```
+
+Will create x86_64 brew environment in ~/test/x86_64-homebrew and install glog and gflags formulae there
+
+There are related discussions at https://github.com/orgs/Homebrew/discussions/2843
+and https://stackoverflow.com/questions/70821136/can-i-install-arm64-libraries-on-x86-64-with-homebrew/70822921#70822921