api-docs: update registerBasicAuth (#3623)

Based on this https://www.selenium.dev/blog/2021/a-tour-of-4-authentication/
This feature is currently implemented on top of Selenium 4’s CDP(Chrome DevTools Protocol) support, and so only works on those browser that support that protocol.
That means it won't work in Safari.
And it's not going to solve the Safari basic auth issue in selenium. See https://www.browserstack.com/docs/automate/selenium/basic-http-authentication

lib/api/client-commands/registerBasicAuth.js

@@ -3,6 +3,7 @@ const {Logger} = require('../../utils');
 
 /**
  * Automate the input of basic auth credentials whenever they arise.
+ * This feature is currently implemented on top of Selenium 4’s CDP(Chrome DevTools Protocol) support, and so only works on those browser that support that protocol
  *
  * @example
  *  this.demoTest = function (browser) {