Update how to use addons with Typescript

README.md

@@ -57,7 +57,18 @@ The proposed way to load xterm.js is via the ES6 module syntax.
 import { Terminal } from 'xterm';
 ```
 
-*Note: There are currently no typings for addons so you will need to upcast if using TypeScript, eg. `(<any>xterm).fit()`.*
+*Note: There are currently no typings for addons if they are accessed via extending Terminal prototype, so you will need to upcast if using TypeScript, eg. `(<any>xterm).fit()`.*
+
+It is recommended to import addon function and enhance the terminal on demand. This would have better typing support and is friendly to treeshaking. E.g.:
+
+```typescript
+import { Terminal } from 'xterm';
+import { fit } from 'xterm/lib/addons/fit/fit';
+const xterm = new Terminal();
+
+// Fit the terminal when necessary:
+fit(xterm);
+```
 
 ### Addons