Add docu on s3fsstore.

Include STS example.

docs/index.rst

@@ -132,6 +132,7 @@ Table of contents
    boto
    azure
    gcstorage
+   s3fsstore
    memory
    db
    git

docs/s3fsstore.rst

@@ -0,0 +1,67 @@
+
+S3 Store
+========
+
+The S3FSStore class in the minimalkv library provides a mechanism to interact with an S3-compatible (e.g. AWS or minio) storage system using the s3fs library.
+
+The preferred initialization method is to use the ``get_store_from_url`` function, which will parse the URL and return an instance of the appropriate store class.
+
+Possible options for the URL are (newline separated for readability):
+
+::
+
+    s3://access_key:secret_key@endpoint/bucket
+    [?create_if_missing=true]
+    [&region_name=region-name]
+    [&force_bucket_suffix=true|false]
+    [&session_token=session-token]
+    [&is_sts_credentials=true|false]
+    [&sts_assume_role__RoleArn=role-arn]
+    [&sts_assume_role__RoleSessionName=session-name]
+    [&sts_assume_role__DurationSeconds=duration-in-seconds]
+    [&sts_assume_role__[KEY]=[VALUE]]
+    [&verify=true|false]
+
+::
+
+    from minimalkv import get_store_from_url
+
+    store = get_store_from_url(
+        "s3://access_key_id:secret_access_key@endpoint/bucket-name"
+    )
+    store.put("example-key", b"example content")
+    print(store.get("example-key"))
+
+
+STS Credentials
+===============
+
+::
+
+    from minimalkv import get_store_from_url
+
+    store = get_store_from_url(
+        "s3://access_key_id:secret_access_key@endpoint/bucket-name"
+        "?is_sts_credentials=true"
+        "&sts_assume_role__RoleArn=arn:aws:iam::123456789012:role/MyRole"
+        "&sts_assume_role__RoleSessionName=MySession"
+        "&sts_assume_role__DurationSeconds=900"
+    )
+
+    store.put("example-key", b"example content")
+    print(store.get("example-key"))
+
+
+If you want to pass nested attributes or lists as parameters, you should import
+the ``S3FSStore`` directly, i.e. ``from minimalkv.net.s3fsstore import S3FSStore``.
+
+
+Local Testing
+=============
+
+::
+
+    AWS_PROFILE={$MINIMALKV_PROFILE} pixi run pytest [--log-cli-level=INFO]
+
+Include AWS_PROFILE or provide AWS credentials in the environment variables, otherwise
+integration tests for AWS S3 will be skipped.