Update flit description; add link to rationale

The 1st paragraph describes what Flit is and what it can do.
The 2nd paragraph describes how it works and what is needed (or not) to
use Flit.

Author: pastelmind

source/key_projects.rst

@@ -370,19 +370,18 @@ flit
 `Issues <https://github.com/takluyver/flit/issues>`__ |
 `PyPI <https://pypi.org/project/flit>`__
 
-Flit is a simple way to put Python packages and modules on PyPI. Flit packages
-a single importable module or package at a time, using the import name as the
-name on PyPI. All subpackages and data files within a package are included
-automatically. Flit requires Python 3, but you can use it to distribute modules
-for Python 2, so long as they can be imported on Python 3.
-
-Flit provides its own implementation (instead of calling
-:ref:`distutils`, :ref:`distlib`, or :ref:`twine` abstractions) of PyPI package
-upload functionality. You can use it to quickly set up package
-configuration files for simple packages (instead of manually writing a
-file that works with :ref:`setuptools`), and build and upload packages to
-PyPI. All wheels built by flit are reproducible, which provides added
-verifiability.
+Flit provides a simple way to upload pure Python packages and modules to PyPI.
+It focuses on `making the easy things easy <flit-rationale_>`_ for packaging.
+Flit can generate a configuration file to quickly set up a simple project, build
+source distributions and wheels, and upload them to PyPI. Flit can also produce
+wheels in a reproducible manner, which provides added verifiability.
+
+Flit uses ``pyproject.toml`` to configure a project. Flit does not rely on tools
+such as :ref:`setuptools` to build distributions, or :ref:`twine` to upload them
+to PyPI. Flit requires Python 3, but you can use it to distribute modules for
+Python 2, so long as they can be imported on Python 3.
+
+.. _flit-rationale: https://flit.readthedocs.io/en/latest/rationale.html
 
 .. _enscons: