Add Github CLI package (#4091)

This adds the Github CLI tool 'gh' as a new package.

Tested on ARM.

packages/github_cli.rb

+require 'package'
+
+class Github_cli < Package
+  description 'Official Github CLI tool'
+  homepage 'https://cli.github.com/'
+  version '0.9.0'
+  source_url 'https://github.com/cli/cli/archive/v0.9.0.tar.gz'
+  source_sha256 '318295e5a662f785662751f1e2cd4b1f613ec3aced1c4e7f1755d27922dbfdbf'
+
+  binary_url ({
+  })
+  binary_sha256 ({
+  })
+
+  depends_on 'go' => :build
+
+  def self.build
+    system 'make'
+  end
+
+  def self.install
+    system "install -Dm755 bin/gh #{CREW_DEST_PREFIX}/bin/gh"
+  end
+end