Adding Gboard Physical Handwriting in the gallery (#901)

Add a web demo of Gboard Physical Handwriting (https://landing.google.co.jp/tegaki) as one application of TensorFlow.js.

GALLERY.md

@@ -33,6 +33,7 @@ Please reach out to us if you'd like to put your project on the list.
 - [GAN Lab](https://poloclub.github.io/ganlab/) - An Interactive Visualization Tool for Playing with Generative Adversarial Networks (GANs)!
 - [Canvas Friends](https://www.y8.com/games/canvas_friends) - Half game, half experiment to see if software can improve the drawing and artistic skills of people.
 - [High School Level Tensorflowjs](http://rocksetta.com/tensorflowjs/) - Greater than 40 demos that can be online edited made as simply as possible using single web pages. All examples use the [<script src="https://cdn.jsdelivr.net/npm/@tensorflow/tfjs">](https://cdn.jsdelivr.net/npm/@tensorflow/tfjs@latest/dist/tf.js) specific version tag so the pages always work and no installation is needed - By Jeremy Ellis.
+- [Gboard Physical Handwriting Version](https://landing.google.co.jp/tegaki/) - You can input a character by drawing it on your keyboard.
 
 ## Tutorials