Reduce package size

Author: shilman

package.json

@@ -1,5 +1,5 @@
 {
-  "version": "4.0.0",
+  "version": "4.0.0-beta.3",
   "name": "babel-plugin-react-docgen",
   "description": "Babel plugin to add react-docgen info into your code",
   "repository": "https://github.com/storybooks/babel-plugin-react-docgen",
@@ -8,6 +8,10 @@
     "Charles Lehnert"
   ],
   "main": "lib/index.js",
+  "files": [
+    "*.md",
+    "lib/**/*"
+  ],
   "devDependencies": {
     "@babel/cli": "^7.6.4",
     "@babel/core": "^7.6.4",