Work towards #56: Splitting up the README

I did the job and splitted up the readme, hopefully everything was
splitted correctly...

servant/index.md

@@ -0,0 +1,17 @@
+---
+layout: pattern
+title: Servant
+folder: servant
+categories: pattern_cat
+tags: pattern_tag
+---
+
+**Intent:** Servant is used for providing some behavior to a group of classes.
+Instead of defining that behavior in each class - or when we cannot factor out
+this behavior in the common parent class - it is defined once in the Servant.
+
+![alt text](./etc/servant-pattern.png "Servant")
+
+**Applicability:** Use the Servant pattern when
+
+* when we want some objects to perform a common action and don't want to define this action as a method in every class.