readme update: tree-shaking

README.md

@@ -21,4 +21,10 @@ let stream$ = new Subject();
 stream$.subscribe(value => console.log(value));
 stream$.next(1); // 1
 stream$.next(2); // 2
+```
+## Tree-shaking
+To perform better tree-shaking, import what you need from its local module, for example:
+```javascript
+import { Subject } from 'rxstream/es5/subjects/subject';
+import { merge } from 'rxstream/es5/operators/merge';
 ```

package.json

@@ -1,6 +1,6 @@
 {
   "name": "rxstream",
-  "version": "1.3.3",
+  "version": "1.3.4",
   "description": "",
   "main": "index.js",
   "repository": {