Add additional metadata for the Ed project

This should make the page for the Gem at rubygems.org more useful.

ed..gemspec

@@ -8,10 +8,16 @@ Gem::Specification.new do |spec|
 
   spec.summary       = "A Jekyll theme for minimal editions"
   spec.description   = "Ed is a Jekyll theme designed for textual editors based on minimal computing principles, and focused on legibility, durability, ease and flexibility."
-  spec.homepage      = "http://minicomp.github.io/ed/"
+  spec.homepage      = "https://minicomp.github.io/ed/"
   spec.license       = "MIT"
 
   spec.required_ruby_version = ">= 2.1.0"
+  spec.metadata      = {
+    "bug_tracker_uri" => "https://github.com/minicomp/ed/issues",
+    "changelog_uri"   => "https://github.com/minicomp/ed/releases",
+    "homepage_uri"    => "https://minicomp.github.io/ed/",
+    "source_code_uri" => "https://github.com/minicomp/ed"
+  }
 
   spec.files         = `git ls-files -z`.split("\x0").select { |f| f.match(%r{^(404|assets|optional|_layouts|_includes|_sass|_texts|index|search|about|credits|documentation|atom|Gemfile|LICENSE|README)}i) }