[docs] Automatically redirect pt to pt-BR

The /pt/ is the most used locale used, it's also the most transalted, almost 100%.
It seems safe to enable auto redirection for this locale.

docs/pages/_app.js

@@ -37,7 +37,7 @@ function useFirstRender() {
   return firstRenderRef.current;
 }
 
-acceptLanguage.languages(['en', 'zh']);
+acceptLanguage.languages(['en', 'zh', 'pt']);
 
 function loadCrowdin() {
   window._jipt = [];