Update README for 2.6.2 (#1880)

Author: rayokota

README.md

@@ -134,6 +134,22 @@ The `Producer`, `Consumer` and `AdminClient` are all thread safe.
           confluent-kafka using the instructions in the
           "Install from source" section below.
 
+To use Schema Registry with the Avro serializer/deserializer:
+
+    $ pip install confluent-kafka[avro,schemaregistry]
+
+To use Schema Registry with the JSON serializer/deserializer:
+
+    $ pip install confluent-kafka[json,schemaregistry]
+
+To use Schema Registry with the Protobuf serializer/deserializer:
+
+    $ pip install confluent-kafka[protobuf,schemaregistry]
+
+When using Data Contract rules (including CSFLE) add the `rules`extra, e.g.:
+
+    $ pip install confluent-kafka[avro,schemaregistry,rules]
+
 **Install from source**
 
 For source install, see the *Install from source* section in [INSTALL.md](INSTALL.md).