DOC: Add security note for Excel export with formula cells

Author: Geronimo Bergk

pandas/core/generic.py

@@ -2252,6 +2252,12 @@ def to_excel(
         and cell character count does not exceed Excel's limitations.
         All other limitations must be checked by the user.
 
+        Excel treats any cell starting with `=` as a formula, which can pose security
+        risks. To store such content as plain text, prepend an apostrophe (`'`), e.g.,
+        change `"=foobar"` to `"'=foobar"`. For `xlsxwriter`, you can use
+        `engine_kwargs={"options": {"strings_to_formulas": False}}` to disable formula
+        interpretation without prepending an apostrophe.
+
         Examples
         --------