Reviewr is a shortcode driven plugin that will allow you to add it easily. Below are the shortcode options:
[reviewr id="1"] - This will display the review of the post id specified. If used as
[reviewr], the current post review will be displayed.
[reviewr-reviews id="1"] - This will display the approved ratings and review of the specified post id. if used as
[reviewr-reviews] the current post reviews will be displayed.