added simulation to README (#15)

Signed-off-by: frederik <[email protected]>

README.md

@@ -1,2 +1,35 @@
 # PX4-gazebo-models
 Models and worlds to be used in local Fuel instances and kept up to date in [app.gazebosim.org/PX4](https://app.gazebosim.org/PX4).
+
+## Starting GZ simulation
+In addition to providing resource files for all models and worlds, this repo also contains a simulation-gazebo script that will start a world and works in conjunction with PX4.
+
+:::note
+In order for this script to work, you must have installed gz-garden beforehand. The way to do this can be found [here](https://gazebosim.org/docs/garden/install_ubuntu):
+:::
+
+After setting up gazebo, navigate to the repo containing simulation-gazebo and script with
+
+```shell
+python simulation-gazebo
+```
+
+If you do not provide any arguments, this will download all models and worlds from the PX4-gazebo-models repo, save them to `/.simulation-gazebo` and start a default world.
+
+The following arguments can be passed:
+
+`--world` A string variable that names the sdf file which runs the simulation world. Default argument is "default", which links to the default world.
+
+`--gz_partition` A string variable that sets the gazebo partition to run in (more information [here]([https://gazebosim.org/api/transport/13/envvars.html))
+
+`--gz_ip` A string variable that sets the IP of the outgoing network interface (more information [here]([https://gazebosim.org/api/transport/13/envvars.html))
+
+`--interactive` A boolean variable that requires the ability to run the code in interactive mode, allowing for custom paths for `--model_download_source`. If this is not set, `--model_download_source` will only download from the default Github repo.
+
+`--model_download_source` A string variable setting the path to a directory from where models are to be imported. At the moment this can only be a local file directory or a http address. The source should end with the zipped resource file. (e.g. https://path/to/simulation/models/resource.zip)
+
+`--model_store` A string variable setting the path to the model storage directory. This is where the zip file provided in `model_download_source` will be placed.
+
+`--overwrite` A boolean variable providing the ability to overwrite existing directories with new data.
+
+`--dryrun` A boolean variable that can be set when running testcases. It will not provide any interactivity and will not start Gazebo simulation.