Add instructions for generating QR codes for links

Install:

```
conda create -n qrcodes python=3.9
conda activate qrcodes
```

```
pip install pyqrcode pypng pyqrcodeng
```

Usage:

```bash
conda activate qrcodes
```

```python
import pyqrcodeng
qr = pyqrcodeng.create('URL', version=8)
# PNG
qr.png(open('workshop_qr.png', 'wb'), scale=10)
# SVG
qr.svg(open('workshop_qr.svg', 'wb'), scale=1)
```
