Add HOW_TO_ARTIFACT

Dockerfile

+FROM python:3.9-slim@sha256:a321a8513911c55888b9c1cc981a5ba646271447a82ece1b62e4a6a8ff1d431b
+
+COPY . .
+
+RUN python3 -m pip install -r tool-cav/requirements.txt

HOW_TO_ARTIFACT.md

+# How to Create Artifact as Docker Image
+
+This is a brief summary of the steps to produce the artifiact docker image.
+
+1) Create a new directory `docker-dir`.
+2) Copy the code into `docker-dir` in its own directory and rename it to `too-cav`.
+3) Move the docker file `Dockerfile` in `docker-dir`.
+4) Remove this file `HOW_TO_ARTIFACT.md`.
+5) In case you ran experiments, remove added directories like `__pycache__` or `venv`, 
+evaluation files in `evaluation_data`, and generated global types in `global_types`.
+6) Run the following command to generate the docker image (potentially with `sudo`):
+    ```bash
+    sudo docker build -t docker-tool-cav
+    ```
+7) To save the image, run the following command:
+    ```bash 
+    docker save docker-tool-cav:latest > docker-tool-cav.tar
+    ```
+8) If you like, you can compress `docker-tool-cav.tar`.