Include .md files as source of rdoc

Author: kateinoigakukun

tasks/doc.rake

@@ -4,5 +4,5 @@ require 'ruby_wasm/version'
 RDoc::Task.new do |doc|
   doc.main = 'README.md'
   doc.title = "ruby.wasm #{RubyWasm::VERSION} Documentation"
-  doc.rdoc_files = FileList.new %w[lib/**/*.rb ext/**/*.c ext/**/*.rb]
+  doc.rdoc_files = FileList.new %w[*.md lib/**/*.rb ext/**/*.c ext/**/*.rb]
 end