Work towards #56: Splitting up the README

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

repository/index.md

@@ -0,0 +1,26 @@
+---
+layout: pattern
+title: Repository
+folder: repository
+categories: pattern_cat
+tags: pattern_tag
+---
+
+**Intent:** Repository layer is added between the domain and data mapping
+layers to isolate domain objects from details of the database access code and
+to minimize scattering and duplication of query code. The Repository pattern is
+especially useful in systems where number of domain classes is large or heavy
+querying is utilized.
+
+![alt text](./etc/repository.png "Repository")
+
+**Applicability:** Use the Repository pattern when
+
+* the number of domain objects is large
+* you want to avoid duplication of query code
+* you want to keep the database querying code in single place
+* you have multiple data sources
+
+**Real world examples:** 
+
+* [Spring Data](http://projects.spring.io/spring-data/)