Add link to tuning cheat sheet

sun.md

diff --git a/sun.md b/sun.md
index 0ce8394..8e80d51 100644
--- a/sun.md
+++ b/sun.md
@@ -56,6 +56,8 @@
 which summarizes the most important factors, gerrit.config options
 and formula.
 
+[Performance Tuning Cheat Sheet](http://bit.ly/1kmpO7V)
+
 *Johannes Nicolai, CollabNet*
 
 ## 12:30 pm Lunch