Add a design doc for decoupling the client code out of SQLFlow Core (#2136)
Add a design doc for decoupling the client code out of SQLFlow Core (#2136)

* Add a design doc for decoupling the client code out of SQLFlow Core

* Revised as comment

* Revised as comments
sql-machine-learning/sqlflow,sql-machine-learning/sqlflow,sql-machine-learning/sqlflow,sql-machine-learning/sqlflow,sql-machine-learning/sqlflow,sql-machine-learning/sqlflow