Merge pull request aws#6971 from justindho/add-low-level-s3-docs-link

Add link to low-level S3 API docs

Author: justindho

awscli/examples/s3/_concepts.rst

@@ -1,5 +1,9 @@
 This section explains prominent concepts and notations in the set of high-level S3 commands provided.
 
+If you are looking for the low level S3 commands for the CLI, please see the
+``s3api`` command `reference page
+<https://docs.aws.amazon.com/cli/latest/reference/s3api/index.html>`_.
+
 Path Argument Type
 ++++++++++++++++++