Add entr package

packages/entr.rb

+require 'package'
+
+class Entr < Package
+  description 'Run arbitrary commands when files change'
+  homepage 'http://entrproject.org/'
+  version '3.9'
+  source_url 'http://entrproject.org/code/entr-3.9.tar.gz'
+  source_sha256 '02d78f18ae530e64bfbb9d8e0250962f85946e10850dd065899d03af15f26876'
+
+  binary_url ({
+  })
+  binary_sha256 ({
+  })
+
+  def self.build
+    system 'cp Makefile.linux Makefile'
+    system "PREFIX=#{CREW_PREFIX} make"
+  end
+
+  def self.install
+    system "make", "DESTDIR=#{CREW_DEST_DIR}", "install"
+  end
+end