org-manual: Do not use #+findex inside Footnote

* doc/org-manual.org (Timestamps):
(Footnotes): Move #+findex entries to the footnote reference.  They do
not work when in Footnote section.

doc/org-manual.org

@@ -5883,6 +5883,12 @@ the agenda (see [[*Weekly/daily agenda]]).  We distinguish:
 
   #+cindex: diary style timestamps
   #+cindex: sexp timestamps
+  # Mentioned inside the footnote.
+  #+findex: org-date
+  #+findex: org-anniversary
+  #+findex: org-cyclic
+  #+findex: org-block
+
   For more complex date specifications, Org mode supports using the
   special expression diary entries implemented in the Emacs Calendar
   package[fn:60].  For example, with optional time:
@@ -22281,11 +22287,6 @@ format]].  The day name is optional when you type the date yourself.
 However, any date inserted or modified by Org adds that day name, for
 reading convenience.
 
-#+findex: org-date
-#+findex: org-anniversary
-#+findex: org-cyclic
-#+findex: org-block
-
 [fn:60] When working with the standard diary expression functions, you
 need to be very careful with the order of the arguments.  That order
 depends evilly on the variable ~calendar-date-style~.  For example, to