Update parsing.mdx to use day.js document website

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Please visit our website https://day.js.org for more information.

docs/pages/getting-started/parsing.mdx

@@ -12,7 +12,7 @@ Material-UI pickers relies on the date management library when the date should b
 Find more information about parsing dates in the documentation for your library:
 
 - [date-fns](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date#Several_ways_to_create_a_Date_object)
-- [dayjs](https://github.com/iamkun/dayjs/blob/dev/docs/en/API-reference.md#constructor-dayjsexisting-string--number--date--dayjs)
+- [dayjs](https://day.js.org/docs/en/parse/parse)
 - [luxon](https://moment.github.io/luxon/docs/manual/parsing.html)
 - [moment](https://momentjs.com/docs/#/parsing/)