Post: small post about "latest core requirements"

Announce the changes made at
readthedocs/readthedocs.org#10508

Note that we are not exposing this feature flag to our users.
We don't want them to contact us to enable this flag.
If they need to install the latest versions they can just specify them in their
`requirements.txt` file.

Author: humitos

python-core-requirements-changed.rst

@@ -0,0 +1,25 @@
+.. post:: July 7, 2023
+   :tags: builders
+   :author: Manuel
+   :location: BCN
+   :category: Changelog
+
+Python "core requirements" installed by default have changed
+============================================================
+
+Starting on **August 7, 2023** all new projects imported on Read the Docs
+will install only ``sphinx``, ``mkdocs`` and ``readthedocs-sphinx-ext`` as "core requirements".
+Besides, the new behavior will install the latest version of these requirements.
+
+Note that previously Read the Docs was installing also
+``jinja``, ``sphinx-rtd-theme``, ``pillow``, ``mock``, ``alabaster``, ``commonmark`` and ``recommonmark``
+specifying particular versions depending on different factors that were confusing for users and hard to debug.
+
+We are moving away from executing commands and installing dependencies on behalf of the users
+and trying to make the build experience on Read the Docs the same as building locally,
+without surprises.
+
+Projects imported previous to August 7, 2023 will keep the actual behavior and won't be affected by this change.
+If you have a project you want to install the latest version of these requirements,
+you can use a ``requirements.txt`` file to specify their versions.
+Read more about :doc:`how to use a requirements.txt file in our documentation <readthedocs:config-file/v2>`.