README link from project home page

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

app/models/repository.rb

@@ -133,6 +133,7 @@ class Repository
     Rails.cache.delete(cache_key(:tag_names))
     Rails.cache.delete(cache_key(:commit_count))
     Rails.cache.delete(cache_key(:graph_log))
+    Rails.cache.delete(cache_key(:readme))
   end
 
   def graph_log
@@ -159,4 +160,10 @@ class Repository
   def blob_at(sha, path)
     Gitlab::Git::Blob.find(self, sha, path)
   end
+
+  def readme
+    Rails.cache.fetch(cache_key(:readme)) do
+      Tree.new(self, self.root_ref).readme
+    end
+  end
 end

app/views/projects/show.html.haml

@@ -31,6 +31,12 @@
             %span Download
           = link_to project_compare_index_path(@project, from: @repository.root_ref, to: @ref || @repository.root_ref), class: 'btn btn-block' do
             Compare code
+
+        - if @repository.readme
+          - readme = @repository.readme
+          = link_to project_blob_path(@project, tree_join(@repository.root_ref, readme.name)), class: 'btn btn-block' do
+            = readme.name
+
     .prepend-top-10
       %p
         %span.light Created on