Add gem install bundler to installation guide

Created by: pschultz

bundler was missing when I followed this guide. Ubuntu points you to the ruby-bundler, which is based on ruby 1.8 and doesn't work. Installing bundler with gem works.

This PR adds the command to do that to the installation guide.

app/models/repository.rb

@@ -151,7 +151,7 @@ class Repository
     return nil unless commit
     # Build file path
-    file_name = self.path_with_namespace + "-" + commit.id.to_s + ".tar.gz"
+    file_name = self.path_with_namespace.gsub("/","_") + "-" + commit.id.to_s + ".tar.gz"
     storage_path = Rails.root.join("tmp", "repositories")
     file_path = File.join(storage_path, file_name)