Add a Python bindings tutorial example that uses JIT and an autoscheduler?

[lirenzhucn]

I was trying to figure out how to use the Python bindings to do some quick prototyping. And naturally, I wanted to start with an auto-scheduler. I kept running into an "unknown autoscheduler name" error. It took me a whole day to find out this 2-year old issue: #6791, and found out about hl.load_plugin.

I think it would be very helpful to newcomers (especially those with more Python experience than C++) to have a tutorial example that uses JIT and an autoscheduler. Because, I believe that is the most natural and lowest-barrier-to-entry way of starting one's Halide experience.

[steven-johnson]

We'd love to have more tutorials for the Python bindings! Unfortunately none of the core contributors has the bandwidth to do this at the present time, but we'd love to review a PR that adds or improves the Python tutorials.