Explain: Brew install (#940)

Author: mathiash98

README.md

@@ -26,12 +26,19 @@ With GitUp, you get a truly efficient Git client for Mac:
 Getting Started
 ===============
 
-**Learn all about GitUp and download the latest release from http://gitup.co.**
+- Official website: https://gitup.co
+
+## Download:
+
+- Latest release on GitHub: https://github.com/git-up/GitUp/releases
+- Homebrew (Not maintained by GitUp developers): `brew install homebrew/cask/gitup` (Note: There is already a formula called gitup, so the full name must be specified!)
 
 **Read the [docs](https://github.com/git-up/GitUp/wiki) and use [GitHub Issues](https://github.com/git-up/GitUp/issues) for support & feedback.**
 
 Releases notes are available at https://github.com/git-up/GitUp/releases. Builds tagged with a `v` (e.g. `v1.2.3`) are released on the "Stable" channel, while builds tagged with a `b` (e.g. `b1234`) are only released on the "Continuous" channel. You can change the update channel used by GitUp in the app preferences.
 
+## Build
+
 To build GitUp yourself, simply run the command `git clone --recursive https://github.com/git-up/GitUp.git` in Terminal, then open the `GitUp/GitUp.xcodeproj` Xcode project and hit Run.
 
 **IMPORTANT:** If you do not have an Apple ID with a developer account for code signing Mac apps, the build  will fail with a code signing error. Simply delete the "Code Signing Identity" build setting of the "Application" target to work around the issue: