Docs: Update OpenAIGen docstrings and add missing headers (#8105)

* update docstrings

* Update haystack/components/generators/openai.py

Co-authored-by: Daria Fokina <daria.fokina@deepset.ai>

---------

Co-authored-by: Daria Fokina <daria.fokina@deepset.ai>

haystack/components/generators/openai.py

@@ -18,25 +18,21 @@ logger = logging.getLogger(__name__)
 @component
 class OpenAIGenerator:
     """
-    Text generation component using OpenAI's large language models (LLMs).
+    Generates text using OpenAI's large language models (LLMs).
 
-    Enables text generation using OpenAI's large language models (LLMs). It supports gpt-4 and gpt-3.5-turbo
-    family of models.
+    It works with the gpt-4 and gpt-3.5-turbo models and supports streaming responses
+    from OpenAI API. It uses strings as input and output.
 
-    Users can pass any text generation parameters valid for the `openai.ChatCompletion.create` method
-    directly to this component via the `**generation_kwargs` parameter in __init__ or the `**generation_kwargs`
-    parameter in `run` method.
+    You can customize how the text is generated by passing parameters to the
+    OpenAI API. Use the `**generation_kwargs` argument when you initialize
+    the component or when you run it. Any parameter that works with
+    `openai.ChatCompletion.create` will work here too.
 
-    For more details on the parameters supported by the OpenAI API, refer to the OpenAI
-    [documentation](https://platform.openai.com/docs/api-reference/chat).
 
-    Key Features and Compatibility:
-     - Primary Compatibility: Designed to work seamlessly with gpt-4, gpt-3.5-turbo family of models.
-     - Streaming Support: Supports streaming responses from the OpenAI API.
-     - Customizability: Supports all parameters supported by the OpenAI API.
+    For details on OpenAI API parameters, see
+    [OpenAI documentation](https://platform.openai.com/docs/api-reference/chat).
 
-     Input and Output Format:
-      - String Format: This component uses the strings for both input and output.
+    ### Usage example
 
     ```python
     from haystack.components.generators import OpenAIGenerator
@@ -65,12 +61,12 @@ class OpenAIGenerator:
         max_retries: Optional[int] = None,
     ):
         """
-        Creates an instance of OpenAIGenerator. Unless specified otherwise in the `model`, OpenAI's GPT-3.5 is used.
+        Creates an instance of OpenAIGenerator. Unless specified otherwise in `model`, uses OpenAI's GPT-3.5.
 
         By setting the 'OPENAI_TIMEOUT' and 'OPENAI_MAX_RETRIES' you can change the timeout and max_retries parameters
         in the OpenAI client.
 
-        :param api_key: The OpenAI API key.
+        :param api_key: The OpenAI API key to connect to OpenAI.
         :param model: The name of the model to use.
         :param streaming_callback: A callback function that is called when a new token is received from the stream.
             The callback function accepts StreamingChunk as an argument.

haystack/components/retrievers/in_memory/embedding_retriever.py

@@ -20,7 +20,7 @@ class InMemoryEmbeddingRetriever:
     In indexing pipelines, use a DocumentEmbedder to embed documents.
     In query pipelines, use a TextEmbedder to embed queries and send them to the retriever.
 
-    Usage example:
+    ### Usage example
     ```python
     from haystack import Document
     from haystack.components.embedders import SentenceTransformersDocumentEmbedder, SentenceTransformersTextEmbedder

haystack/components/writers/document_writer.py

@@ -16,7 +16,7 @@ class DocumentWriter:
     """
     Writes documents to a DocumentStore.
 
-    Usage example:
+    ### Usage example
     ```python
     from haystack import Document
     from haystack.components.writers import DocumentWriter