Update AutoML user guide to document linkage between sort_metric and stopping_metric


User guide currently says this for `stopping_metric` : "AUTO: This defaults to logloss for classification and deviance for regression."

This is TRUE iff sort_metric is not set, but if sort_metric is set, then we automatically set stopping_metric to the same thing. The exception is when `sort_metric = "AUC"` in which we will set `stopping_metric = "logloss"`.


Erin LeDell

Fix versions


Erin LeDell