Fixed code examples (#1)

`render` return promise, so await it.

Author: iBobik

content/1.getting-started/3.usage.md

@@ -40,7 +40,7 @@ You can use the `pretty` option to beatify the output.
 import { MyTemplate } from './email';
 import { render } from '@vue-email/render';
 
-const html = render(MyTemplate,{
+const html = await render(MyTemplate,{
   title: 'some title',
 },{
   pretty: true,
@@ -73,7 +73,7 @@ Here’s how to convert a Vue component into plain text.
 import { MyTemplate } from './email';
 import { render } from '@vue-email/render';
 
-const text = render(MyTemplate, {
+const text = await render(MyTemplate, {
   title: 'some title',
 }, {
   plainText: true,