Add DATEDIF disclaimer (#5686)

Asterisk for DATEIF function, doesn't show as a regular function, but can still be used.

src/data/roadmaps/data-analyst/content/101-excel/100-basic-functions/110-datedif.md

@@ -1,3 +1,5 @@
 # DATEDIF
 
 The `DATEDIF` function is an incredibly valuable tool for a Data Analyst in Excel or Google Sheets, by providing the ability to calculate the difference between two dates. This function takes in three parameters: start date, end date and the type of difference required (measured in years, months, days, etc.). In Data Analysis, particularly when dealing with time-series data or when you need to uncover trends over specific periods, the `DATEDIF` function is a necessary asset. Recognizing its functionality will enable a data analyst to manipulate or shape data progressively and efficiently.
+
+* `DATEDIF` is technically still supported, but wont show as an option. For additional information, see Excel "Help" page.