Add documentation about pyproject.toml

Author: rgaiacs

docs/source/configuration/development.md

@@ -24,10 +24,22 @@ environment. Our
 [example `requirements.txt` file](https://github.com/binder-examples/requirements/blob/HEAD/requirements.txt)
 on GitHub shows a typical requirements file.
 
+(pyproject)=
+
+## `pyproject.toml` - Install Python packages
+
+To install your reprository like a Python package, you may include a
+`pyproject.toml` file. `repo2docker`install `pyproject.toml` files by running
+`pip install -e .`.
+
 (setup-py)=
 
 ## `setup.py` - Install Python packages
 
+```{note}
+We recommend to use `pyproject.toml` as it is the recommended way since 2020 when PEPs [621](https://peps.python.org/pep-0621/) and [631](https://peps.python.org/pep-0631/) were accepted.
+```
+
 To install your repository like a Python package, you may include a
 `setup.py` file. `repo2docker` installs `setup.py` files by running
 `pip install -e .`.