Write something about GDAL

README.md

@@ -44,6 +44,26 @@ $ source .venv/bin/activate
 $ pip install -r requirements.txt
 ```
 
+### The curious case of GDAL
+
+It's really hard to install GDAL. We need it to generate the tiles for the map.
+Here is one way to do it but you might run into problems and need to research a
+bit.
+
+```bash
+$ sudo apt install -y libgdal-dev
+$ pip install pygdal=="`gdal-config --version`.*"
+$ pip install gdal2tiles
+```
+
+And then it should be possible to run the tile generation.
+
+```bash
+$ gdal2tiles.py -l -p raster -z 0-5 -w none tiles2
+```
+
+You may need to use `python gdal2tiles.py` instead?
+
 ### Run the server
 
 ```bash