docs: improve example template

Author: m-muecke

man-roxygen/example.R

@@ -3,5 +3,17 @@
 #' <%= sprintf("learner = lrn(\"%s\")", id) %>
 #' print(learner)
 #'
-#' # available parameters:
-#' learner$param_set$ids()
+#' # Define a Task
+#' task = tsk("usarrests")
+#'
+#' # Train the learner on the task
+#' learner$train(task)
+#'
+#' # Print the model
+#' print(learner$model)
+#'
+#' # Make predictions for the task
+#' prediction = learner$predict(task)
+#'
+#' # Score the predictions
+#' prediction$score(task = task)