docs: update netlify form (#1126)

Author: razonyang

exampleSite/content/docs/layouts/contact/index.md

@@ -64,7 +64,9 @@ It is designed to be compatible with most backends, such as [Netlify form](https
 
 ### Netlify
 
-[Netlify form](https://docs.netlify.com/forms/setup) are supported out of box, therefore, you don't need to specify the `contact.endpoint` parameter.
+[Netlify form](https://docs.netlify.com/forms/setup) are supported out of box, you MUST not to specify the `contact.endpoint` parameter.
+
+Please configure the `SITE_RECAPTCHA_KEY` and `SITE_RECAPTCHA_SECRET` environment variables if reCAPTCHA 2 is enabled, see also [Custom reCAPTCHA 2](https://docs.netlify.com/forms/spam-filters/#custom-recaptcha-2).
 
 > The demo site uses Getform instead of Netlify form, because the Netlify will upgrade your form level automatically if you exceed the limit of current plan, which will lead to additional expenses.
 

exampleSite/content/docs/layouts/contact/index.zh-hans.md

@@ -63,7 +63,9 @@ layout = "contact"
 
 ### Netlify
 
-[Netlify form](https://docs.netlify.com/forms/setup) 可开箱即用，因此，你无需指定 `contact.endpoint` 参数。
+[Netlify form](https://docs.netlify.com/forms/setup) 可开箱即用，你不应该指定 `contact.endpoint` 参数。
+
+当启用 reCAPTCHA 2 时，请配置 `SITE_RECAPTCHA_KEY` 和 `SITE_RECAPTCHA_SECRET` 环境变量，详情请参阅 [Custom reCAPTCHA 2](https://docs.netlify.com/forms/spam-filters/#custom-recaptcha-2)。
 
 > 演示站点使用 Getform 而不是 Netlify form，因为当你超过当前套餐限定时， Netlify 会自动升级你的套餐，这会导致额外的支出。
 

exampleSite/content/docs/layouts/contact/index.zh-hant.md

@@ -63,7 +63,9 @@ layout = "contact"
 
 ### Netlify
 
-[Netlify form](https://docs.netlify.com/forms/setup) 可開箱即用，囙此，你無需指定 `contact.endpoint` 參數。
+[Netlify form](https://docs.netlify.com/forms/setup) 可開箱即用，你不應該指定 `contact.endpoint` 參數。
+
+當啟用 reCAPTCHA 2 時，請配置 `SITE_RECAPTCHA_KEY` 和 `SITE_RECAPTCHA_SECRET` 環境變量，詳情請參閱 [Custom reCAPTCHA 2](https://docs.netlify.com/forms/spam-filters/#custom-recaptcha-2)。
 
 > 演示網站使用 Getform 而不是 Netlify form，因為當你超過當前套餐限定時，Netlify 會自動升級你的套餐，這會導致額外的支出。