Add source code and changelog links to gemspec

geocoder.gemspec

@@ -18,4 +18,9 @@ Gem::Specification.new do |s|
   s.require_paths = ["lib"]
   s.executables = ["geocode"]
   s.license     = 'MIT'
+
+  s.metadata = {
+    'source_code_uri' => 'https://github.com/alexreisner/geocoder',
+    'changelog_uri'   => 'https://github.com/alexreisner/geocoder/blob/master/CHANGELOG.md'
+  }
 end