Update docs: add post meta date localization info

Author: Vimux

exampleSite/content/docs/customization.md

@@ -80,6 +80,16 @@ Full list of available default post meta fields:
 In addition to the default meta fields, you can add your own by placing a custom partial under
 `layouts/partials/post_meta/<name>.html`.
 
+#### Post meta: `date` localization
+
+With [Hugo v0.87.0](https://gohugo.io/news/0.87.0-relnotes/) (or later), `date` meta field shows localized dates (with
+weekdays and months in the current language) by default. In most cases, such a transition is painless, but owners of
+multilingual sites should be careful and check that everything translates as expected after the upgrade.
+
+You can also use a predefined layout, like `:date_full`, and it will output localized dates or times. For additional
+information about localized dates and possible date/time formatting layouts, please see
+[Hugo: time.Format](https://gohugo.io/functions/dateformat/).
+
 ### Thumbnail visibility
 
 By default, a thumbnail image has shown for a list and single pages simultaneously. In some cases, you may want to show