[PECO-1803] Remove sqlalchemy and update README.md (#469)

Remove sqlalchemy and update README.md

Signed-off-by: Jacky Hu <[email protected]>

CONTRIBUTING.md

@@ -144,9 +144,6 @@ The `PySQLStagingIngestionTestSuite` namespace requires a cluster running DBR ve
 
 The suites marked `[not documented]` require additional configuration which will be documented at a later time.
 
-#### SQLAlchemy dialect tests
-
-See README.tests.md for details.
 
 ### Code formatting
 

README.md

@@ -3,9 +3,9 @@
 [![PyPI](https://img.shields.io/pypi/v/databricks-sql-connector?style=flat-square)](https://pypi.org/project/databricks-sql-connector/)
 [![Downloads](https://pepy.tech/badge/databricks-sql-connector)](https://pepy.tech/project/databricks-sql-connector)
 
-The Databricks SQL Connector for Python allows you to develop Python applications that connect to Databricks clusters and SQL warehouses. It is a Thrift-based client with no dependencies on ODBC or JDBC. It conforms to the [Python DB API 2.0 specification](https://www.python.org/dev/peps/pep-0249/) and exposes a [SQLAlchemy](https://www.sqlalchemy.org/) dialect for use with tools like `pandas` and `alembic` which use SQLAlchemy to execute DDL. Use `pip install databricks-sql-connector[sqlalchemy]` to install with SQLAlchemy's dependencies. `pip install databricks-sql-connector[alembic]` will install alembic's dependencies.
+The Databricks SQL Connector for Python allows you to develop Python applications that connect to Databricks clusters and SQL warehouses. It is a Thrift-based client with no dependencies on ODBC or JDBC. It conforms to the [Python DB API 2.0 specification](https://www.python.org/dev/peps/pep-0249/).
 
-This connector uses Arrow as the data-exchange format, and supports APIs to directly fetch Arrow tables. Arrow tables are wrapped in the `ArrowQueue` class to provide a natural API to get several rows at a time.
+This connector uses Arrow as the data-exchange format, and supports APIs (e.g. `fetchmany_arrow`) to directly fetch Arrow tables. Arrow tables are wrapped in the `ArrowQueue` class to provide a natural API to get several rows at a time. [PyArrow](https://arrow.apache.org/docs/python/index.html) is required to enable this and use these APIs, you can install it via  `pip install pyarrow` or `pip install databricks-sql-connector[pyarrow]`.
 
 You are welcome to file an issue here for general use cases. You can also contact Databricks Support [here](help.databricks.com).
 
@@ -22,7 +22,7 @@ For the latest documentation, see
 
 ## Quickstart
 
-Install the library with `pip install databricks-sql-connector`
+Install the library with `pip install databricks-sql-connector[pyarrow]`
 
 ```bash
 export DATABRICKS_HOST=********.databricks.com