chore: Add security issue notification to readme (#137)

* chore: Add security issue notification to readme

* chore: Fix anchor in README.rst.

Sphinx linkcheck seems to error if the anchor doesn't exactly match the id= value, even if the anchor itself works.

Co-authored-by: Matt Bullock <[email protected]>
Co-authored-by: lizroth <[email protected]>

Author: 3 people

README.rst

@@ -39,6 +39,8 @@ full documents in our `primary documents`_.
 
 You can find our source on `GitHub`_.
 
+`Security issue notifications`_
+
 ***************
 Getting Started
 ***************
@@ -193,3 +195,4 @@ of the one that the client would normally construct for you.
 .. _CryptoConfig: https://aws-dynamodb-encryption-python.readthedocs.io/en/latest/lib/encrypted/config.html
 .. _decrypt_dynamodb_item: https://aws-dynamodb-encryption-python.readthedocs.io/en/latest/lib/encrypted/item.html#dynamodb_encryption_sdk.encrypted.item.decrypt_dynamodb_item
 .. _transformation functions: https://aws-dynamodb-encryption-python.readthedocs.io/en/latest/lib/tools/transform.html
+.. _Security issue notifications: https://github.com/aws/aws-dynamodb-encryption-python/blob/master/CONTRIBUTING.md#user-content-security-issue-notifications