feat: add Vietnamese translation (#548)

* Create vi.ts

Create i18n Vietnamese translation file.

* Update translation.ts

Added Vietnamese language support.

* Update config.ts

Add Vietnamese (vi) to be a possible value for the `lang` key.

* Create README.vi.md

Created Vietnamese version of README.

* Update README.md

Added navigation/link to Vietnamese version of README.

* Update README.md

fixed a mistake

src/config.ts

@@ -10,7 +10,7 @@ import { LinkPreset } from "./types/config";
 export const siteConfig: SiteConfig = {
 	title: "Fuwari",
 	subtitle: "Demo Site",
-	lang: "en", // 'en', 'zh_CN', 'zh_TW', 'ja', 'ko', 'es', 'th'
+	lang: "en", // 'en', 'zh_CN', 'zh_TW', 'ja', 'ko', 'es', 'th', 'vi'
 	themeColor: {
 		hue: 250, // Default hue for the theme color, from 0 to 360. e.g. red: 0, teal: 200, cyan: 250, pink: 345
 		fixed: false, // Hide the theme color picker for visitors