Add section about custom template

Author: jakubno

README.md

@@ -218,3 +218,23 @@ urllib3==1.26.7
 xarray==2024.2.0
 xlrd==2.0.1
 ```
+
+### Custom template using Code Interpreter
+
+The template requires custom setup. If you want to build your own custom template and use Code Interpreter, you need to do:
+1. Copy `jupyter_server_config.py` and `start-up.sh` from this PR
+2. Add following commands in your Dockerfile
+```Dockerfile
+# Installs jupyter server and kernel
+RUN pip install jupyter-server ipykernel ipython
+RUN ipython kernel install --name "python3" --user
+# Copes jupyter server config
+COPY ./jupyter_server_config.py /home/user/.jupyter/
+# Setups jupyter server
+COPY ./start-up.sh /home/user/.jupyter/
+RUN chmod +x /home/user/.jupyter/start-up.sh
+```
+3. Add the following option `-c "/home/user/.jupyter/start-up.sh"` to `e2b template build` command or add this line to your `e2b.toml`. 
+```yaml
+start_cmd = "/home/user/.jupyter/start-up.sh"
+```