Doc update readme (graphql-python#114)

* import_transports_directly_from_gql

* DOC Update README.md

* Add warnings regarding 2.x version
* Better explanation on how to use a local schema
* Example of GraphQL query using variable values
* Very brief example of the DSL module
* Improved Async advanced usage example
* Added backoff module for retries in the advanced example
* Removed RequestsHTTPTransport example

* fix indentation

* Revert "import_transports_directly_from_gql"

This reverts commit bfe72a3.

Removing PR graphql-python#112 from this PR ...