Update README.md

README.md

@@ -17,7 +17,7 @@ With Filby you have a change log, comprising a sequence of reference data 'chang
 <br/>
 Like checking out a commit, your applications can use the Filby API to retrieve a desired set of reference data for a given change set id. They can also inspect the changelog to find which change set was in effect at a given point in time, and be notified when the reference data they are interested in changes.
 
-## Contents
+## Concepts
 - [Introduction](#introduction)
 - [How it works](#how-it-works)
 - [API](#api)
@@ -137,7 +137,7 @@ Refering back to the previous list of challenges:
 - **Evolution** of reference data is supported by versioned entities and projections
 - **Local Testing** is possible through HTTP mocking libraries.
 
-## How it works
+## Concepts
 filby has the following important concepts
 <pre>
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