docs: describe how to set up a dev environment (#18)

### Summary of Changes

Add documentation how to set up a dev environment, run the tests, and
build the documentation.

docs/development/environment.md

@@ -0,0 +1,33 @@
+# Environment
+
+This document describes how to configure and use your development environment.
+
+!!! note
+
+    All terminal commands listed below are assumed to be run from the root of the repository.
+
+## Initial setup
+
+1. Install [Python 3.10](https://www.python.org/downloads/).
+2. Install [poetry](https://python-poetry.org/docs/master/#installation).
+3. Install dependencies of this project by running this command:
+    ```shell
+    poetry install
+    ```
+
+## Running the tests
+
+1. Run this command:
+    ```shell
+    poetry run pytest
+    ```
+
+## Serving the documentation
+
+1. Start the server by running this command:
+    ```shell
+    poetry run mkdocs serve
+    ```
+2. Check the command output for the URL of the created site and open it in a browser (usually [localhost:8000](http://localhost:8000)).
+
+You can keep the server running while you edit the documentation. The server will automatically rebuild and reload the site when you save changes.

mkdocs.yml

@@ -7,6 +7,8 @@ nav:
   - Examples:
     - Titanic: examples/titanic.md
   - API Reference: reference/
+  - Development:
+    - Environment: development/environment.md
 
 # Configuration of MkDocs & Material for MkDocs --------------------------------