updated README: encourage merge requests

README.md

 # Quantum Information course 2021
 This is a collection of programming tasks and scripts used in the lecture on quantum information theory in summer semester 2021 at RWTH University.
 
+If you want to improve the programs in this repository, feel free to open a merge request or an issue.
+
 All files in this repository for which no other license is specified may be reused under the terms of the MIT license.