chore: updated readme regarding mongodb_ecto, fixed some specs

Author: zookzook

README.md

@@ -30,6 +30,17 @@
 - support for streaming protocol ([See](https://github.com/mongodb/specifications/blob/master/source/server-discovery-and-monitoring/server-monitoring.rst#streaming-protocol))
 - support for migration scripts
 
+## mongodb_ecto
+
+The version 1.4.0 supports the [mongodb_ecto](https://github.com/elixir-mongo/mongodb_ecto) package. 
+A series of changes are required to support the adapter. Some BSON encoders and a missing generic update function were added for the adapter. 
+Most notably, the `find-then-modify` command functions `find_one_and_update` and `find_one_and_replace` now return appropriate 
+`FindAndModifyResult` structs that contain additional write information otherwise neglected, which the adapter requires. 
+
+After upgrading the driver to version 1.4.0 you need to change the code regarding the results of 
+* `Mongo.find_one_and_update`
+* `Mongo.find_one_and_replace`
+
 ## Usage
 
 ### Installation
@@ -38,7 +49,7 @@ Add `mongodb_driver` to your mix.exs `deps`.
 
 ```elixir
 defp deps do
-  [{:mongodb_driver, "~> 1.0.0"}]
+  [{:mongodb_driver, "~> 1.4.0"}]
 end
 ```
 

lib/mongo.ex

@@ -474,7 +474,7 @@ defmodule Mongo do
           BSON.document(),
           BSON.document(),
           Keyword.t()
-        ) :: result(BSON.document()) | {:ok, nil}
+        ) :: result(Mongo.FindAndModifyResult.t()) | {:ok, nil}
   def find_one_and_update(topology_pid, coll, filter, update, opts \\ []) do
     _ = modifier_docs(update, :update)
 
@@ -537,7 +537,7 @@ defmodule Mongo do
           BSON.document(),
           BSON.document(),
           Keyword.t()
-        ) :: result(BSON.document())
+        ) :: result(Mongo.FindAndModifyResult.t())
   def find_one_and_replace(topology_pid, coll, filter, replacement, opts \\ []) do
     _ = modifier_docs(replacement, :replace)