doc: develop: manifests: external: add emlearn

Introduce documentation for using emlearn (TinyML library) as an
external module in Zephyr.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

doc/develop/manifest/external/emlearn.rst

@@ -0,0 +1,52 @@
+.. _external_module_emlearn:
+
+emlearn
+#######
+
+Introduction
+************
+
+`emlearn`_ is an open source library for deploying machine learning models on micro-controllers
+and embedded systems. It provides portable C code generation from models trained with
+scikit-learn or Keras.
+
+A Python library allows converting complex machine learning models to a minimal C code
+representation, which enables running ML inference on resource-constrained embedded devices.
+
+emlearn is licensed under the MIT license.
+
+Usage with Zephyr
+*****************
+
+The emlearn repository is a Zephyr :ref:`module <modules>` which provides TinyML capabilities to
+Zephyr applications, allowing machine learning models to be run directly on Zephyr-powered devices.
+
+To pull in emlearn as a Zephyr module, either add it as a West project in the ``west.yaml``
+file or pull it in by adding a submanifest (e.g. ``zephyr/submanifests/emlearn.yaml``) file
+with the following content and run ``west update``:
+
+.. code-block:: yaml
+
+   manifest:
+     projects:
+       - name: emlearn
+         url: https://github.com/emlearn/emlearn.git
+         revision: master
+         path: modules/lib/emlearn # adjust the path as needed
+
+For more detailed instructions and API documentation, refer to the `emlearn documentation`_, and in
+particular the `Getting Started on Zephyr RTOS`_ section.
+
+References
+**********
+
+.. target-notes::
+
+.. _emlearn:
+   https://github.com/emlearn/emlearn
+
+.. _emlearn documentation:
+   https://emlearn.readthedocs.io/en/latest/
+
+.. _Getting Started on Zephyr RTOS:
+   https://emlearn.readthedocs.io/en/latest/getting_started_zephyr.html