add AUR link and description to README

There is an AUR in the repositories which makes it easy
to install and update pretty maps

README.md

@@ -24,12 +24,22 @@ This work is [licensed](LICENSE) under a GNU Affero General Public License v3.0
 
 ## Installation
 
+### PIP
+
 Install with
 
 ```
 $ pip install prettymaps
 ```
 
+### Arch Linux
+
+Use the [AUR](https://aur.archlinux.org/packages/python-prettymaps/)
+
+```
+yay -S python-prettymaps
+```
+
 ## Usage example (For more examples, see [this Jupyter Notebook](https://nbviewer.jupyter.org/github/marceloprates/prettymaps/blob/main/notebooks/examples.ipynb)):
 
 ```python