Add License Section in README.md

Add GPLv3 section with link to the license text.

README.md

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+[![License: GPL v3](https://img.shields.io/badge/License-GPL%20v3-blue.svg)](http://www.gnu.org/licenses/gpl-3.0)
 <h1 align="center">EGOA - Energy Grid Optimization and Analysis</h1>
 
 Energy Grid Optimization and Analysis (EGOA) is a framework for energy grid analysis and planning.
 
-License|Linux & macOS Build
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-[![License: GPL v3](https://img.shields.io/badge/License-GPL%20v3-blue.svg)](http://www.gnu.org/licenses/gpl-3.0)|[![Travis-CI Status](https://travis-ci.org/franziska-wegner/egoa.svg?branch=master)](https://travis-ci.org/franziska-wegner/egoa)
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 <h2>Installation</h2>
 
 This is a Cmake project and can be run in any C++ IDE (Integrated Development Environment) that is on the market and supports CMake. You have to define a certain set of parameters dependent on your system and what you wish to run in general. The following will help you with the initial setup and links to the frameworks that can be linked in addition.
@@ -275,3 +271,9 @@ This repository is based on the PhD thesis <a href="http://dx.doi.org/10.5445/IR
 https://www.doxygen.nl
 https://github.com/franziska-wegner/PhD_Thesis--Combinatorial_Problems_in_Energy_Networks--Graph_Theoretic_Models_and_Algorithms
 http://dx.doi.org/10.5445/IR/1000120612
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+<h2>License</h2>
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+This work---including recursively all subfolder contents and files---is licensed under <a href="https://www.gnu.org/licenses/gpl-3.0.html">GNU General Public License (GPL) v3</a>.
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+<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/9/93/GPLv3_Logo.svg/2880px-GPLv3_Logo.svg.png" width="100" />