clarify requirements for sorting string dates

Author: guimachiavelli

learn/filtering_and_sorting/working_with_dates.mdx

@@ -14,7 +14,7 @@ In this guide, you will learn about Meilisearch's approach to date and time valu
 
 ## Preparing your documents
 
-To filter and sort search results chronologically, your documents must have at least one field containing either a [UNIX timestamp](https://kb.narrative.io/what-is-unix-time) or a date in a human readable format such as `"2025-01-13"`.
+To filter and sort search results chronologically, your documents must have at least one field containing a [UNIX timestamp](https://kb.narrative.io/what-is-unix-time). You may also use a string with a date in a format that can be sorted lexicographically, such as `"2025-01-13"`.
 
 As an example, consider a database of video games. In this dataset, the release year is formatted as a timestamp: