message: docs: fix i18n guide typo
  Fixes
  PR Close
diff: @@ -431,7 +431,7 @@ Follow these steps:
  > <code-example path="i18n/doc-files/messages.fr.xlf.html" region="translated-hello-before" header="src/locale/messages.fr.xlf (&lt;trans-unit&gt;)"></code-example>
  -> The `id="introductionHeader""` is a [custom ID](#custom-id "Manage marked text with custom IDs"), but without the `@@` prefix required in the source HTML.
  +> The `id="introductionHeader"` is a [custom ID](#custom-id "Manage marked text with custom IDs"), but without the `@@` prefix required in the source HTML.
  2. Duplicate the `<source>...</source>` element in the text node, rename it `target`, and then replace its content with the French text:
  