docs: better headings (#29)

### Summary of Changes

The term "stdlib" makes sense from the perspective of the entire
project. For someone who just wants to use the Python components,
however, we should instead talk about the "Safe-DS Python Library".

docs/README.md

@@ -1,4 +1,4 @@
-# Safe-DS Stdlib
+# Safe-DS Python Library
 
 [![PyPI](https://img.shields.io/pypi/v/safe-ds)](https://pypi.org/project/safe-ds/)
 [![Main](https://github.com/Safe-DS/Stdlib/actions/workflows/main.yml/badge.svg)](https://github.com/Safe-DS/Stdlib/actions/workflows/main.yml)

mkdocs.yml

@@ -1,4 +1,4 @@
-site_name: Safe-DS Stdlib
+site_name: Safe-DS Python Library
 repo_url: https://github.com/Safe-DS/Stdlib
 repo_name: Safe-DS/Stdlib
 

src/README.md

@@ -1,7 +1,7 @@
-# Safe-DS Stdlib
+# Safe-DS Python Library
 
 [![PyPI](https://img.shields.io/pypi/v/safe-ds)](https://pypi.org/project/safe-ds/)
-[![Main](https://github.com/lars-reimann/Safe-DS/actions/workflows/main.yml/badge.svg)](https://github.com/Safe-DS/Stdlib/actions/workflows/main.yml)
+[![Main](https://github.com/Safe-DS/Stdlib/actions/workflows/main.yml/badge.svg)](https://github.com/Safe-DS/Stdlib/actions/workflows/main.yml)
 [![codecov](https://codecov.io/gh/Safe-DS/Stdlib/branch/main/graph/badge.svg?token=HVRP1633B1)](https://codecov.io/gh/Safe-DS/Stdlib)
 [![Documentation Status](https://readthedocs.org/projects/safe-ds-stdlib/badge/?version=latest)](https://safe-ds-stdlib.readthedocs.io/en/latest/?badge=latest)