Update docstring for GenerationNode.gen & fit (facebook#2245)

Summary:
Pull Request resolved: facebook#2245

--

Reviewed By: lena-kashtelyan

Differential Revision: D54506927

fbshipit-source-id: ef1f0bcb0b4b38f597344d7cae45691ed9c3c31d

ax/modelbridge/generation_node.py

@@ -256,8 +256,15 @@ def fit(
         the model kwargs set on each corresponding model spec and the kwargs
         passed to this method.
 
-        NOTE: Local kwargs take precedence over the ones stored in
-        ``ModelSpec.model_kwargs``.
+        Args:
+            experiment: The experiment to fit the model to.
+            data: The experiment data used to fit the model.
+            search_space: An optional overwrite for the experiment search space.
+            optimization_config: An optional overwrite for the experiment
+                optimization config.
+            kwargs: Additional keyword arguments to pass to the model's
+                ``fit`` method. NOTE: Local kwargs take precedence over the ones
+                stored in ``ModelSpec.model_kwargs``.
         """
         self._model_spec_to_gen_from = None
         for model_spec in self.model_specs:
@@ -283,21 +290,27 @@ def gen(
         alongside any kwargs passed in to this function (with local kwargs)
         taking precedent.
 
+        NOTE: Models must have been fit prior to calling ``gen``.
+        NOTE: Some underlying models may ignore the ``n`` argument and produce a
+            model-determined number of arms. In that case this method will also output
+            a generator run with number of arms that may differ from ``n``.
+
         Args:
-            n: Optional nteger representing how many arms should be in the generator
+            n: Optional integer representing how many arms should be in the generator
                 run produced by this method. When this is ``None``, ``n`` will be
                 determined by the ``ModelSpec`` that we are generating from.
             pending_observations: A map from metric name to pending
                 observations for that metric, used by some models to avoid
                 resuggesting points that are currently being evaluated.
-            max_gen_draws_for_deduplication: TODO
+            max_gen_draws_for_deduplication: Maximum number of attempts for generating
+                new candidates without duplicates. If non-duplicate candidates are not
+                generated with these attempts, a ``GenerationStrategyRepeatedPoints``
+                exception will be raised.
             model_gen_kwargs: Keyword arguments, passed through to ``ModelSpec.gen``;
                 these override any pre-specified in ``ModelSpec.model_gen_kwargs``.
 
-        NOTE: Models must have been fit prior to calling ``gen``.
-        NOTE: Some underlying models may ignore the ``n`` argument and produce a
-            model-determined number of arms. In that case this method will also output
-            a generator run with number of arms (that can differ from ``n``).
+        Returns:
+            A ``GeneratorRun`` containing the newly generated candidates.
         """
         model_spec = self.model_spec_to_gen_from
         should_generate_run = True