Register *.md to default's mime_types.rb in Rails to fix 文字化け like:

cf. https://coderdojo.jp/docs/*.md

Author: yasulab

config/initializers/mime_types.rb

@@ -2,3 +2,7 @@
 
 # Add new mime types for use in respond_to blocks:
 # Mime::Type.register "text/richtext", :rtf
+
+# MarkdownファイルのMIMEタイプを設定
+Mime::Type.register 'text/markdown', :md, %w( text/plain )
+Rack::Mime::MIME_TYPES['.md'] = 'text/markdown; charset=utf-8'