Properly render plain readme

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/generic/typography.scss

@@ -17,6 +17,14 @@ pre {
     background: #333;
     color: $background-color;
   }
+
+  &.plain-readme {
+    background: none;
+    border: none;
+    padding: 0;
+    margin: 0;
+    font-size: 14px;
+  }
 }
 .monospace {

app/helpers/application_helper.rb

@@ -213,6 +213,10 @@ module ApplicationHelper
       Haml::Helpers.preserve(markdown(file_content))
     elsif asciidoc?(file_name)
       asciidoc(file_content)
+    elsif plain?(file_name)
+      content_tag :pre, class: 'plain-readme' do
+        file_content
+      end
     else
       GitHub::Markup.render(file_name, file_content).
         force_encoding(file_content.encoding).html_safe
@@ -221,6 +225,10 @@ module ApplicationHelper
     simple_format(file_content)
   end
+  def plain?(filename)
+    Gitlab::MarkupHelper.plain?(filename)
+  end
+
   def markup?(filename)
     Gitlab::MarkupHelper.markup?(filename)
   end

lib/gitlab/markup_helper.rb

@@ -33,6 +33,16 @@ module Gitlab
       filename.downcase.end_with?(*%w(.adoc .ad .asciidoc))
     end
+    # Public: Determines if the given filename is plain text.
+    #
+    # filename - Filename string to check
+    #
+    # Returns boolean
+    def plain?(filename)
+      filename.downcase.end_with?('.txt') ||
+        filename.downcase == 'readme'
+    end
+
     def previewable?(filename)
       markup?(filename)
     end