[BUG] Documentation doesn't explain what this project is

[dblock]

What is the bug?
The fork didn't carry a README that explains what this project is, why it exists or how to use it.

Do you have any additional context?
I came from opensearch-project/opensearch-py#90, and it took me a while to figure out what the difference between opensearch-py and opensearch-dsl-py is.

[elfisher]

@VijayanB what are your thoughts on adding a sentence to the readme that outlines what this dsl client is used for. Something like "opensearch-dsl-py is a python client specifically used for build and running queries against OpenSearch."

[VijayanB]

@elfisher Agree. I will create a PR to update the same.

[wbeckler]

@VijayanB Did you create the PR for changing the README?