Update docstring

Author: tadeja

cpp/src/arrow/compute/api_vector.h

@@ -309,8 +309,8 @@ class ARROW_EXPORT InversePermutationOptions : public FunctionOptions {
   /// of the input indices minus 1 and the length of the function's output will be the
   /// length of the input indices.
   int64_t max_index = -1;
-  /// \brief Optional type of the output inverse permutation. Default of `nullopt` will
-  /// use the same type as the input indices, otherwise must be signed integer type. An
+  /// \brief The data type for the output array of inverse permutation. Defaults to the
+  /// type of the input indices when `nullopt`. Must be a signed integer type. An
   /// invalid error will be reported if this type is not able to store the length of the
   /// input indices.
   std::optional<std::shared_ptr<DataType>> output_type;