HomebrewFormula: add Homebrew formula

HomebrewFormula/age.rb

@@ -0,0 +1,21 @@
+# Copyright 2019 Google LLC
+#
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file or at
+# https://developers.google.com/open-source/licenses/bsd
+
+class Age < Formula
+  desc "Simple, modern, secure file encryption"
+  homepage "https://filippo.io/age"
+  url "https://github.com/FiloSottile/age/archive/v1.0.0-beta1.zip"
+  sha256 "6c7b1de0f312bc6e17e6b26ec27598672d1064e0287f202da5ab7efa9a1bb9d8"
+
+  depends_on "go" => :build
+
+  def install
+    ENV["GOPATH"] = HOMEBREW_CACHE/"go_cache"
+    system "mkdir", bin
+    system "go", "build", "-o", bin, "filippo.io/age/cmd/..."
+    prefix.install_metafiles
+  end
+end