Post: Drop support for "Use system packages" (#235)

* Post: Drop support for "Use system packages"

Announcement of readthedocs/readthedocs.org#10562

* Update drop-support-system-packages.rst

Co-authored-by: Eric Holscher <[email protected]>

---------

Co-authored-by: Eric Holscher <[email protected]>

Author: humitos

drop-support-system-packages.rst

@@ -0,0 +1,45 @@
+.. post:: August 8, 2023
+   :tags: builders
+   :author: Manuel
+   :location: BCN
+   :category: Changelog
+
+Drop support for "Use system packages"
+======================================
+
+
+Read the Docs used to pre-install common scientific Python packages like ``scipy``, ``numpy``, ``pandas``, ``matplotlib`` and others
+at system level to speed up the build process.
+However, with all the work done in the Python ecosystem and the introduction of "wheels",
+these packages are a lot easier to install via ``pip install`` and these pre-installed packages are not required anymore.
+If you have Apt package dependencies,
+they can be installed with `build.apt_packages <https://docs.readthedocs.io/en/stable/config-file/v2.html#build-apt-packages>`_.
+
+With the introduction of our new "Ubuntu 20.04" and "Ubuntu 22.04" Docker images,
+we stopped pre-installing these extra Python packages and we encouraged users to install and pin all their dependencies using a ``requirements.txt`` file.
+We have already stopped supporting "use system packages" on these newer images.
+
+**We are removing the "use system packages" feature on August 29th**.
+Make sure you are installing all the required dependecies to build your project's documentation using a ``requirements.txt`` file and specifying it in your ``.readthedocs.yaml``.
+
+Here you have an example of the section required on the ``.readthedocs.yaml`` configuration file:
+
+.. code-block:: yaml
+
+   python:
+     install:
+       - requirements: docs/requirements.txt
+
+
+The content of ``docs/requirements.txt`` would be similar to::
+
+    scipy==1.11.1
+    numpy==1.25.2
+    pandas==2.0.3
+    matplotlib==3.7.2
+
+Read more about this in our :doc:`introduction to Reproducible Builds <readthedocs:guides/reproducible-builds>` guide for more details.
+
+Please, `contact us`_ and let us know any inconvenient you may have with this change.
+
+.. _contact us: mailto:[email protected]