Add README for advanced workshop

advanced/README.md

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+# Git Course for Advanced
+This folder contains the exercises for the C2SM Git Workshop "Git for Advanced".
+Feel free to download the material to practice and enhance your Git skills.
+
+The corresponding [slides of this course](https://wiki.c2sm.ethz.ch/CM/WorkshopBestPractices2013) can be found
+at the C2SM wiki.
+
+Each exercise is located in this folder.
+
+## How to run the exercises
+First of all, you need a Git installation on your computer.
+To do so, please follow the [instructions from GitHub](https://github.com/git-guides/install-git).
+
+> **_Important note:_**  You must have at least Git 2.28 (released 27 July 2020) installed. 
+> You can check your Git version by typing `git --version` in your terminal.
+
+Second, you need a Python installation as well.
+We provide you here with [instructions from realpython](https://realpython.com/installing-python/),
+but of course many other instruction will do it as well.
+
+Now, use your own terminal to go through the exercises, which are all desecribed in the Markdown files.
+
+**Have fun!**