Not supported for non-Google direct dependencies

Author: paulb777

README.md

@@ -4,6 +4,8 @@ This repository is a copy of https://github.com/firebase/abseil-cpp with
 the git metadata removed to provide one to two orders of magnitude increase in
 speed for Swift Package Manager usage.
 
+This repo is not supported as a direct dependency for non-Google usage.
+
 There should be no changes to this repo other than updates from its mirror
 and Swift Package Manager specific items.