Improved documentation for the private option (#2086)

* Improved documentation for the private option

* Updating docstring

* updating incorrect wording

qiskit_ibm_runtime/runtime_options.py

@@ -70,7 +70,12 @@ def __init__(
                 this time limit, it is forcibly cancelled. Simulator jobs continue to use wall
                 clock time.
             session_time: Length of session in seconds.
-            private: Boolean of whether or not the job is marked as private.
+            private: Boolean that indicates whether the job is marked as private. This is only
+                supported for ``ibm_quantum`` channel. When set to true, input parameters are not
+                returned, and the results can only be read once. After the results are read or after
+                a specified time after the job is completed, the results are deleted from the service.
+                When set to false, the input parameters and results follow the standard retention
+                behavior.
         """
         self.backend = backend
         self.image = image