fix: Update reason documentation with inExperiment value

Author: jsonbailey

ldclient/evaluation.py

@@ -54,6 +54,11 @@ def reason(self) -> dict:
         * ``errorKind``: further describes the nature of the error if the kind was ``ERROR``,
           e.g. ``"FLAG_NOT_FOUND"``
 
+        * ``inExperiment``: True if the evaluation was part of an experiment. This is set when
+          the evaluation resulted in the context being assigned to a variation that is part of a
+          running experiment. This property is used by LaunchDarkly's Experimentation product to
+          track experiment assignment events.
+
         * ``bigSegmentsStatus``: describes the validity of Big Segment information, if and only if
           the flag evaluation required querying at least one Big Segment; otherwise it returns None.
           Allowable values are defined in :class:`BigSegmentsStatus`. For more information, read the