Add podspec

Down.podspec

@@ -0,0 +1,13 @@
+Pod::Spec.new do |spec|
+  spec.name         = "Down"
+  spec.summary      = "Blazing fast Markdown rendering in Swift, built upon cmark."
+  spec.version      = "0.1"
+  spec.homepage     = "https://github.com/iwasrobbed/Down"
+  spec.license      = { :type => "MIT", :file => "LICENSE" }
+  spec.authors      = { "Rob Phillips" => "rob@desideratalabs.co" }
+  spec.source       = { :git => "https://github.com/iwasrobbed/Down.git", :tag => "v" + spec.version.to_s }
+  spec.source_files = "Source/**/*"
+  spec.platform		= :ios, "9.0"
+  spec.requires_arc = true
+  spec.module_name = "Down"
+end