Updated design of the "API Reference" text
Here is an example of the current format:
It changed to
`langchain.retrievers.ElasticSearchBM25Retriever` format. The same
format as it is in the API Reference Toc.
It also resembles code:
`from langchain.retrievers import ElasticSearchBM25Retriever` (namespace
THEN class_name)
Current format is
`ElasticSearchBM25Retriever from langchain.retrievers` (class_name THEN
namespace)
This change is in line with other formats and improves readability.
@baskaryan
