Start adding an overview page for contributors

Author: rheitjoh

contributors/getting-started.md

@@ -1 +1,16 @@
-# Getting started as a contributor
+---
+title: Contributing to Cryptimeleon libraries
+toc: true
+---
+
+We are glad you are interested in contributing to Cryptimeleon.
+This page will give you an overview of our contribution/developer guidelines and will point you to further information.
+
+## Overview
+
+The Cryptimeleon libraries consist of a number of related cryptographic libraries united under the Cryptimeleon name.
+If you want to contribute, you therefore first need to decide on a specific library.
+Then you can check out that library's issue tracker (we use the Github issue tracker) to find something to work on.
+
+
+