readme: setup github pages to overcome 512k limit

asciidoctor/link-target-github.rb

@@ -0,0 +1,19 @@
+#!/usr/bin/env ruby
+#
+# https://github.com/cirosantilli/linux-kernel-module-cheat#asciidoctor-link-target-up-rb
+
+require 'asciidoctor'
+require 'asciidoctor/extensions'
+
+require_relative 'link-target-up.rb'
+
+class LinkTargetGitHub < LinkTargetUp
+  named :link
+  def target_base
+    'https://github.com/cirosantilli/linux-kernel-module-cheat/blob/master/'
+  end
+end
+
+Asciidoctor::Extensions.register do
+  inline_macro LinkTargetGitHub
+end