Specific use-case: adding packages via requirements.txt in compose

docs/apache-airflow/howto/docker-compose/index.rst

@@ -271,6 +271,40 @@ to rebuild the images on-the-fly when you run other ``docker compose`` commands.
 Examples of how you can extend the image with custom providers, python packages,
 apt packages and more can be found in :doc:`Building the image <docker-stack:build>`.
 
+Special case - adding dependencies via requirements.txt file
+============================================================
+
+Usual case for custom images, is when you want to add a set of requirements to it - usually stored in
+``requirements.txt`` file. For development, you might be tempted to add it dynamically when you are
+starting the original airflow image, but this has a number of side effects (for example your containers
+will start much slower - each additional dependency will further delay your containers start up time).
+Also it is completely unnecessary, because docker compose has the development workflow built-in.
+You can - following the previous chapter, automatically build and use your custom image when you
+iterate with docker compose locally. Specifically when you want to add your own requirement file,
+you should do those steps:
+
+1) Comment out the ``image: ...`` line and remove comment from the ``build: .`` line in the
+   ``docker-compose.yaml`` file. The relevant part of the docker-compose file of yours should look similar
+   to (use correct image tag):
+
+```
+#image: ${AIRFLOW_IMAGE_NAME:-apache/airflow:2.5.1}
+build: .
+```
+
+2) Create ``Dockerfile`` in the same folder your ``docker-compose.yaml`` file is with content similar to:
+
+```
+FROM apache/airflow:2.5.1
+ADD requirements.txt .
+RUN pip install -r requirements.txt
+```
+
+3) Place ``requirements.txt`` file in the same directory.
+
+Run ``docker compose build`` to build the image, or add ``--build`` flag to ``docker compose up`` or
+``docker compose run`` commands to build the image automatically as needed.
+
 Networking
 ==========