Resolve "Update installation instructions"

Closes #50 (closed)

• Cherry-pick 344701b5
• delete branch 50-update-installation-instructions
• in CONTRIBUTING.md add info on how to update PROD repo (currently at gitlab.ethz.ch)

environment_linux.yml

+# Open a terminal and execute the following command to create the conda environment
+# for the workshop
+# 'conda env create -f environment_linux.yml'
+
+name: machine_learning_workshop_2021
+
+channels:
+  - anaconda
+  - defaults
+
+dependencies:
+  - python==3.8.8
+  - pandas
+  - matplotlib
+  - scikit-learn==0.24.1
+  - seaborn
+  - jupyterlab==3.1.7
+  - pydot
+  - pillow
+  - pip
+  - tensorflow==2.4.1