docs ecosystem/integrations update 4 (#5590)

# docs `ecosystem/integrations` update 4

Added missed integrations. Fixed inconsistencies. 

## Who can review?

@hwchase17 
@dev2049

docs/integrations/cohere.md

@@ -1,25 +1,38 @@
 # Cohere
 
-This page covers how to use the Cohere ecosystem within LangChain.
-It is broken into two parts: installation and setup, and then references to specific Cohere wrappers.
+>[Cohere](https://cohere.ai/about) is a Canadian startup that provides natural language processing models
+> that help companies improve human-machine interactions.
 
 ## Installation and Setup
-- Install the Python SDK with `pip install cohere`
-- Get an Cohere api key and set it as an environment variable (`COHERE_API_KEY`)
+- Install the Python SDK :
+```bash
+pip install cohere
+```
 
-## Wrappers
+Get a [Cohere api key](https://dashboard.cohere.ai/) and set it as an environment variable (`COHERE_API_KEY`)
 
-### LLM
+
+## LLM
 
 There exists an Cohere LLM wrapper, which you can access with 
+See a [usage example](../modules/models/llms/integrations/cohere.ipynb).
+
 ```python
 from langchain.llms import Cohere
 ```
 
-### Embeddings
+## Text Embedding Model
 
-There exists an Cohere Embeddings wrapper, which you can access with 
+There exists an Cohere Embedding model, which you can access with 
 ```python
 from langchain.embeddings import CohereEmbeddings
 ```
 For a more detailed walkthrough of this, see [this notebook](../modules/models/text_embedding/examples/cohere.ipynb)
+
+## Retriever
+
+See a [usage example](../modules/indexes/retrievers/examples/cohere-reranker.ipynb).
+
+```python
+from langchain.retrievers.document_compressors import CohereRerank
+```