: add Homebrew install instructions to README.md

Closes #76
cuelang/cue#76

GitOrigin-RevId: e74e67d5cf756de7895a60a51d5cf78b0fa101fb
Change-Id: I9de2f4daddd194740ab80d42efd952fd9507690b
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/2949
Reviewed-by: Marcel van Lohuizen <[email protected]>

Author: jlongtine

README.md

@@ -93,6 +93,12 @@ Some aspects of this are:
 
 ### Download and Install
 
+#### Install using Homebrew
+
+Using [Homebrew](https://brew.sh), you can install using the CUE Homebrew tap:
+
+`brew install cuelang/tap/cue`
+
 #### Install From Source
 
 If you already have Go installed, the short version is: