Add note about dev/build behavior to error boundaries docs

I'm using create-react-app and when I use an ErrorBoundary with componentdidcatch and run "npm start," my custom error message briefly flashes as intended, but then the regular developer error page shows after a second or so. There is no mention of this behavior on the docs page, so I spent a lot of time trying to figure out what I did wrong before I tried running the build version and saw it worked as expected (no default error page shown).

找到 Error Boundaries 文档页面，并使用 "npm start" 和 build 版本通过 create-react-app 重现该行为。添加说明，解释在开发环境中开发者错误页面可能会出现在自定义消息之后，而 build 版本的行为符合预期；确认文档与两种模式都一致。