Add missing README descriptions (tensorflow#2204)

README.md

@@ -30,6 +30,9 @@ running TensorFlow 0.12 or earlier, please
 - [neural_programmer](neural_programmer): neural network augmented with logic and mathematic operations.
 - [next_frame_prediction](next_frame_prediction): probabilistic future frame synthesis via cross convolutional networks.
 - [object_detection](object_detection): localizing and identifying multiple objects in a single image.
+- [pcl_rl](pcl_rl): code for several reinforcement learning algorithms, including Path Consistency Learning.
+- [ptn](ptn): perspective transformer nets for 3D object reconstruction.
+- [qa_kg](qa_kg): module networks for question answering on knowledge graphs.
 - [real_nvp](real_nvp): density estimation using real-valued non-volume preserving (real NVP) transformations.
 - [rebar](rebar): low-variance, unbiased gradient estimates for discrete latent variable models.
 - [resnet](resnet): deep and wide residual networks.