Add the first version of workflow design (#956)
Add the first version of workflow design (#956)

* Add the first version of workflow design

* clean up some words:

* Explain motivations

1. Identify shared parts and remove redundant execution.
2. Improve concurrency.

* Add Related Work section

* Update design_workflow.md

* Clean up

* Grammarly.com

sql-machine-learning/sqlflow,sql-machine-learning/sqlflow,sql-machine-learning/sqlflow,sql-machine-learning/sqlflow,sql-machine-learning/sqlflow,sql-machine-learning/sqlflow