Update package description and keywords

Author: adamgraham

README.md

@@ -1,5 +1,7 @@
 # Animation Tweening
 
+The Animation Tweening package provides a system for tweening object properties in Unity.
+
 ## Installation
 
 The Unity Package Manager can load a package from a Git repository on a remote server.

package.json

@@ -2,8 +2,13 @@
   "name": "com.zigurous.animation.tweening",
   "version": "0.1.0",
   "displayName": "Zigurous Animation Tweening",
-  "description": "An animation system for tweening object properties in Unity.",
+  "description": "The Animation Tweening package provides a system for tweening object properties in Unity.",
   "unity": "2019.4",
+  "keywords": [
+    "animation",
+    "tweening",
+    "system"
+  ],
   "repository": "https://github.com/zigurous/unity-animation-tweening",
   "publishConfig": {
     "registry": "https://npm.pkg.github.com/@zigurous"