Update OMPP model addition docs

docs/en/8-MicroSim/Additions.md

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+## Adding a New Model
+
+**Note**: use a notebook with at least 6Gb of memory for this full guide. 
+
+First clone the model's repository or download and extract the archived model on your AAW notebook. In our example, we clone oncosim from [gitlab](../6-Gitlab/Gitlab.md):
+
+![Oncosim dir is now available](image.png)
+
+### Compiling the model
+
+In this case, we are compiling for mpi, so we retrieved the appropriate OMPP release from the [openmpp releases page](https://github.com/openmpp/main/releases). Make sure to use the archived releases provided by openM and not auto-generated by Github. 
+
+We can follow the readme of the model. In this case, we set our `OM_ROOT` environment variable to the same directory as our OMPP release using `export OM_ROOT=~/buckets/aaw-unclassified/microsim/openmpp_ubuntu_mpi_20231115`.
+
+We can now compile. We make sure that we're in the oncosim directory then run `make OM_MSG_USE=MPI RELEASE=1 all publish`. 
+
+Once compilation is complete, our compiled model files appear under `<path-to-model>/ompp-linux/bin/`. Using the terminal, `cp` the files in the `bin` directory to `~/buckets/aaw-unclassified/microsim/models/bin`.
+
+![oncosim model files under bin](image-2.png)
+
+Once complete, run `restart-oms.sh` in the terminal. This will restart the OpenM web service and allow it to pick up the new model.
+
+![model in UI](image-3.png)