Update README

Author: skylander86

README.md

@@ -18,20 +18,23 @@ pip install formsg
 
 The SDK provides two main utility functions for handling FormSG webhook:
 
-- [`verify_signature(webhook_uri, signature_header, signature_expiry_seconds=60)`](formsg/webhook.py) verifies that the incoming webhook's signature is valid based on the FormSG production public key.
+- [`webhook_uri: str, signature_header: str, signature_expiry_seconds: float = 60)`](formsg/utils.py) verifies that the incoming webhook's signature is valid based on the FormSG production public key.
 It raises a `nacl.exceptions.BadSignatureError` if the signature is invalid.
 The signature header is usually found in the `X-FormSG-Signature` header.
 Details on how the signature is constructed can be found [here](https://github.com/opengovsg/formsg-javascript-sdk/#verifying-signatures-manually).
 
-- [`decrypt_content(body_json, secret_key)`](formsg/webhook.py) will decrypt the encrypted content using the given Base-64 encoded secret key.
-`body_json` is expected to be a dictionary-like object.
+- [`decrypt_content(body: Mapping[str, Any], secret_key: str)`](formsg/utils.py) will decrypt the encrypted content using the given Base-64 encoded secret key.
+`body` is expected to be a dictionary-like object.
+
+- [`decrypt_attachment(body: Mapping[str, Any], field_id: str, secret_key: str)`](formsg/utils.py) will decrypt the encrypted content using the given Base-64 encoded secret key.
+`body` is expected to be a dictionary-like object.
 
 For convenience, the SDK implements a [`decrypt_django_request`](formsg/django.py) and [`decrypt_flask_request`](formsg/flask.py) which returns the decrypted FormSG content from a Django/Flask request object directly.
 
 ### Example with Flask
 
 ```python
-from formsg.webhook import decrypt_flask_request
+from formsg.flask import decrypt_flask_request
 
 from flask import Flask
 from flask import jsonify