importmap is not introduced

[Here](https://javascript.info/modules-intro#no-bare-modules-allowed), it says no bare modules are allowed in browsers. However, if you use an [importmap](https://developer.mozilla.org/docs/Web/HTML/Element/script/type/importmap), you can use bare modules in browsers.

Start with the “No bare modules allowed” section of the modules introduction page and review the linked browser module and import map references. Update the explanation so it accurately qualifies the statement about bare modules in browsers, then check that the links and surrounding examples remain consistent.

Written by the indexing model from the issue text.