DOC: How to merge or use multiple retrievers?

[djaffer]

Checklist

• I added a very descriptive title to this issue.
• I included a link to the documentation page I am referring to (if applicable).

Issue with current documentation:

No response

Idea or request for content:

The documentation misses this use case. Based of search seems python has the merger_retriever but js doesn't

[jeasonnow]

The function merge_retrievers similar to Python's has not been implemented yet, but I can submit a PR to achieve this.

[djaffer]

@jeasonnow will this work with elastic vector store?

[jeasonnow]

I believe this applies to all retriever instances. You can try using my code locally to see how it works; the usage is consistent with Python's approach.
@djaffer