chore: update installation documentation

Author: scotwells

README.md

@@ -6,6 +6,22 @@
 
 ## Installing
 
+### Homebrew
+
+The Datum Cloud CLI can be installed using the
+[datum-cloud/tap](https://github.com/datum-cloud/homebrew-tap) tap.
+
+```shell
+$ brew tap datum-cloud/tap
+==> Tapping datum-cloud/tap
+...
+
+$ brew install datum-cloud/tap/cli
+==> Fetching datum-cloud/tap/cli
+```
+
+### Manually
+
 Install the Datum Cloud CLI using the following command.
 
 ```shell