Remove unnecessary method from Qdrant vectorstore and clean up docstrings (#2700)

**Problem:**

The `from_documents` method in Qdrant vectorstore is unnecessary because
it does not change any default behavior from the abstract base class
method of `from_documents` (contrast this with the method in Chroma
which makes a change from default and turns `embeddings` into an
Optional parameter).

Also, the docstrings need some cleanup.

**Solution:**

Remove unnecessary method and improve docstrings.

---------

Co-authored-by: Vijay Rajaram <vrajaram3@gatech.edu>

langchain/vectorstores/qdrant.py

@@ -21,6 +21,7 @@ class Qdrant(VectorStore):
     Example:
         .. code-block:: python
 
+            from qdrant_client import QdrantClient
             from langchain import Qdrant
 
             client = QdrantClient()
@@ -125,7 +126,7 @@ class Qdrant(VectorStore):
             filter: Filter by metadata. Defaults to None.
 
         Returns:
-            List of Documents most similar to the query and score for each
+            List of Documents most similar to the query and score for each.
         """
         embedding = self.embedding_function(query)
         results = self.client.search(
@@ -157,6 +158,7 @@ class Qdrant(VectorStore):
             query: Text to look up documents similar to.
             k: Number of Documents to return. Defaults to 4.
             fetch_k: Number of Documents to fetch to pass to MMR algorithm.
+                     Defaults to 20.
 
         Returns:
             List of Documents selected by maximal marginal relevance.
@@ -201,7 +203,7 @@ class Qdrant(VectorStore):
         metadata_payload_key: str = METADATA_KEY,
         **kwargs: Any,
     ) -> Qdrant:
-        """Construct Qdrant wrapper from raw documents.
+        """Construct Qdrant wrapper from a list of texts.
 
         Args:
             texts: A list of texts to be indexed in Qdrant.
@@ -212,45 +214,50 @@ class Qdrant(VectorStore):
             location:
                 If `:memory:` - use in-memory Qdrant instance.
                 If `str` - use it as a `url` parameter.
-                If `None` - use default values for `host` and `port`.
+                If `None` - fallback to relying on `host` and `port` parameters.
             url: either host or str of "Optional[scheme], host, Optional[port],
                 Optional[prefix]". Default: `None`
             port: Port of the REST API interface. Default: 6333
             grpc_port: Port of the gRPC interface. Default: 6334
             prefer_grpc:
-                If `true` - use gPRC interface whenever possible in custom methods.
-            https: If `true` - use HTTPS(SSL) protocol. Default: `None`
-            api_key: API key for authentication in Qdrant Cloud. Default: `None`
+                If true - use gPRC interface whenever possible in custom methods.
+                Default: False
+            https: If true - use HTTPS(SSL) protocol. Default: None
+            api_key: API key for authentication in Qdrant Cloud. Default: None
             prefix:
-                If not `None` - add `prefix` to the REST URL path.
-                Example: `service/v1` will result in
-                    `http://localhost:6333/service/v1/{qdrant-endpoint}` for REST API.
-                Default: `None`
+                If not None - add prefix to the REST URL path.
+                Example: service/v1 will result in
+                    http://localhost:6333/service/v1/{qdrant-endpoint} for REST API.
+                Default: None
             timeout:
                 Timeout for REST and gRPC API requests.
                 Default: 5.0 seconds for REST and unlimited for gRPC
             host:
                 Host name of Qdrant service. If url and host are None, set to
-                'localhost'. Default: `None`
+                'localhost'. Default: None
             path:
                 Path in which the vectors will be stored while using local mode.
-                Default: `None`
+                Default: None
             collection_name:
                 Name of the Qdrant collection to be used. If not provided,
-                will be created randomly.
+                it will be created randomly. Default: None
             distance_func:
-                Distance function. One of the: "Cosine" / "Euclid" / "Dot".
+                Distance function. One of: "Cosine" / "Euclid" / "Dot".
+                Default: "Cosine"
             content_payload_key:
                 A payload key used to store the content of the document.
+                Default: "page_content"
             metadata_payload_key:
                 A payload key used to store the metadata of the document.
+                Default: "metadata"
             **kwargs:
                 Additional arguments passed directly into REST client initialization
 
         This is a user friendly interface that:
-            1. Embeds documents.
-            2. Creates an in memory docstore
-            3. Initializes the Qdrant database
+            1. Creates embeddings, one for each text
+            2. Initializes the Qdrant database as an in-memory docstore by default
+               (and overridable to a remote docstore)
+            3. Adds the text embeddings to the Qdrant database
 
         This is intended to be a quick way to get started.