docs: add draft on executors

docs/executors.md

@@ -0,0 +1,27 @@
+# Executors - run your workflows
+
+Since `fasthep-flow` is built on top of Apache Airflow, it supports all of the
+executors that Airflow supports. The default executor is the
+[LocalExecutor](#localexecutor), which runs all tasks in parallel on the local
+machine. A full list of executors can be found in the
+[Airflow documentation](https://airflow.apache.org/docs/apache-airflow/stable/executor/index.html).
+
+Since Apache Airflow is not widely used in High Energy Particle Physics, let's
+go over the executors that are most relevant to us.
+
+## LocalExecutor
+
+The `LocalExecutor` (see
+[Airflow docs](https://airflow.apache.org/docs/apache-airflow/stable/core-concepts/executor/local.html))
+runs each task in a separate process on the local machine. This is the default
+executor for `fasthep-flow`.
+
+## DaskExecutor
+
+The `DaskExecutor` (see
+[Airflow docs](https://airflow.apache.org/docs/apache-airflow/stable/core-concepts/executor/dask.html))
+runs each task in a separate process on a Dask cluster. A Dask cluster can be
+run on a local machine or as a distributed cluster using a batch system (e.g.
+HTCondor, LSF, PBS, SGE, SLURM) or other distributed systems such as LHCb's
+DIRAC. This is the recommended executor for running `fasthep-flow` workflows on
+distributed resources.

docs/index.md

@@ -32,12 +32,13 @@ YAML file. More on this under [Configuration](./configuration.md).
 ## Documentation
 
 ```{toctree}
-
 changelog.md
 installation.md
 concepts.md
 configuration.md
 operators.md
+executors.md
 examples/index.md
+advanced_examples/index.md
 developers_corner.md
 ```