Add a README file to the Dash materials

Author: gahjelle

python-dash/README.md

@@ -0,0 +1,23 @@
+# Develop Data Visualization Interfaces in Python With Dash
+
+This folder contains the source code developed in the tutorial [Develop Data Visualization Interfaces in Python With Dash](https://realpython.com/python-dash/).
+
+The folder [`avocado_analytics_3`](avocado_analytics_3/) shows the final state of the source code.
+
+The tutorial uses [`dash`](https://pypi.org/project/dash/) and [`pandas`](https://pypi.org/project/pandas/). You can install these packages by [creating and activating a virtual environment](https://realpython.com/python-virtual-environments-a-primer/) and then running pip:
+
+```console
+(venv) $ python -m pip install dash pandas
+```
+
+Alternatively, You can get an environment with the exact same versions of dependencies as used in the tutorial by installing from [`requirements.txt`](requirements.txt):
+
+```console
+(venv) $ python -m pip install -r requirements.txt
+```
+
+Run the file `app.py` to start your dashboard.
+
+## License
+
+Distributed under the MIT license. See [`LICENSE`](https://github.com/realpython/materials/blob/master/LICENSE) for more information.