Added entries to gitignore for jekyll metadata and gem/bundler files …

…used to render github page locally

.gitignore

@@ -1,3 +1,9 @@
-_site
+# Ignore metadata generated by Jekyll
+_site/
+.sass-cache/
+.jekyll-cache/
+.jekyll-metadata
+
+Gemfile*
 
 *.sublime-*