Add flask docs

docs/source/flask.rst

@@ -0,0 +1,38 @@
+.. _flasking:
+
+**************
+Use with Flask
+**************
+
+A `flask`_ extension is also provided so it's easy to get started with
+developing new web interfaces with calibrestekje. In order to get started
+you'll need to install the extension.
+
+.. _flask: https://flask.palletsprojects.com
+
+.. code-block:: bash
+
+    $ pip install flask-calibrestekje
+
+And then go ahead and create a ``flaskconfig.cfg`` file.
+
+.. code-block:: config
+
+    CALIBRESTEKJE_SQLITE_URL = "sqlite:///mymetadata.db"
+
+And then finally, create your Flask application.
+
+.. code-block:: python
+
+    from calibrestekje import Book
+    from flask import Flask, jsonify
+
+    from flask_calibrestekje import CalibreStekje
+
+    app = Flask(__name__)
+    app.config.from_pyfile("config.cfg")
+    db = CalibreStekje(app)
+
+    @app.route("/")
+    def home():
+        return jsonify({"book-count": db.session.query(Book).count()})

docs/source/index.rst

@@ -9,6 +9,7 @@
    examples
    modules-api
    forking
+   flask
    upgrade
    contribute
    changelog