DOCSP-11519: fixes to MONGODB-AWS auth presentation (#119)

Author: Chris Cho

source/fundamentals/authentication.txt

@@ -23,6 +23,7 @@ MongoDB Community Edition which includes:
 - ``SCRAM-SHA-256``
 - ``SCRAM-SHA-1``
 - ``MONGODB-CR``
+- ``MONGODB-AWS``
 - ``X.509``
 
 The :doc:`Enterprise Authentication Mechanisms 

source/fundamentals/authentication/mechanisms.txt

@@ -12,7 +12,8 @@ Authentication Mechanisms
 
 In this guide, you can find sample code for connection to MongoDB with each
 authentication mechanism available in the MongoDB Community Edition:
-``DEFAULT``, ``SCRAM-SHA-256``, ``SCRAM-SHA-1``, ``MONGODB-CR``, and ``X.509``.
+``DEFAULT``, ``SCRAM-SHA-256``, ``SCRAM-SHA-1``, ``MONGODB-CR``,
+``MONGODB-AWS``, and ``X.509``.
 
 ``DEFAULT``
 -----------
@@ -147,6 +148,13 @@ The driver checks the following sources for your credentials in order:
 4. AWS EC2 endpoint. For more information, see `IAM Roles for Tasks
    <https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task-iam-roles.html>`_.
 
+If you do not already have the `aws signature library <https://www.npmjs.com/package/aws4>`__,
+install it using the following ``npm`` command:
+
+.. code-block:: console
+
+   npm install aws4
+
 The following code shows an example of specifying the ``MONGODB-AWS``
 authentication mechanism and credentials in the connection string.