Add updating homebrew instruction (PowerShell#3533)

docs/maintainers/releasing.md

@@ -255,3 +255,22 @@ Currently the NuGet packages published to [powershell-core feed][ps-core-feed] o
 Maintainers are working on including the assemblies built for non-Windows platforms.
 
 [ps-core-feed]: https://powershell.myget.org/gallery/powershell-core
+
+
+Homebrew
+========
+
+After the release, you can update homebrew formula.
+
+On macOS:
+1. Make sure that you have [homebrew cask](https://caskroom.github.io/).
+1. `brew update`
+1. `cd /usr/local/Homebrew/Library/Taps/caskroom/homebrew-cask/Casks`
+1. Edit `./powershell.rb`, reference [file history](https://github.com/vors/homebrew-cask/commits/master/Casks/powershell.rb) for the guidelines:
+    1. Update `version`
+    1. Update `sha256` to the checksum of produced `.pkg` (note lower-case string for the consistent style)
+    1. Update `checkpoint` value. To do that run `brew cask _appcast_checkpoint --calculate 'https://github.com/PowerShell/PowerShell/releases.atom'`
+1. `brew cask style --fix ./powershell.rb`, make sure there are no errors
+1. `brew cask audit --download ./powershell.rb`, make sure there are no errors
+1. `brew cask reinstall powershell`, make sure that powershell was updates successfully
+1. Commit your changes, send a PR to https://github.com/caskroom/homebrew-cask