Effect handlers Tutorial (#2169)

* init

* cleanup

* gallery

* rerun

* refine

* final corrections

Author: juanitorduz

docs/source/_static/img/tutorials/effect_handlers.png

@@ -28,6 +28,7 @@ NumPyro documentation
    tutorials/bayesian_regression
    tutorials/bayesian_hierarchical_linear_regression
    examples/baseball
+   tutorials/effect_handlers
    examples/vae
    examples/funnel
    examples/stochastic_volatility