Update contribution guidelines

CONTRIBUTING.md

@@ -5,15 +5,23 @@ If you spot a typo or the content does not make sense in some way, feel free to
 I am open for enhancement ideas and feature requests. If there's some topic you'd like to see a notebook about, feel free to open an issue and request it there.
  
 ## Development
+Install development dependencies
+```
+pip install -r dev-requirements.txt
+```
 
-#### post_save_hook
-* Copy the content of utils/post_save_hook.py to your jupyter_notebook_config.py before making changes to notebooks
-* This will setup a post_save_hook which will generate a html version of the notebook automatically when the notebook is saved
-* htmls are not generated for exercises
+#### Generating html
+```
+python scripts/notebook_to_html.py <path-to-ipynb-file>
+```
 
 #### Testing
-* Travis CI will make sure that the code cells in the notebooks can be executed
-* You test the same locally by:
-    * install tox by: `pip install tox`
-    * run tox: `tox`
-* Tests are not run for exercises (because the code in the exercise cells is usually intentionally incomplete)
+```
+pytest --nbval notebooks
+```
+
+#### pre-commit
+```
+pre-commit install
+```
+and it'll automatically run all the pre-commit hooks for each commit.