Document the behaviour of int("NaN")

There are still people surprised by it, e.g.
https://www.perlmonks.org/?node_id=11159579

pod/perlfunc.pod

@@ -3773,8 +3773,10 @@ You should not use this function for rounding: one because it truncates
 towards C<0>, and two because machine representations of floating-point
 numbers can sometimes produce counterintuitive results.  For example,
 C<int(-6.725/0.025)> produces -268 rather than the correct -269; that's
-because it's really more like -268.99999999999994315658 instead.  Usually,
-the L<C<sprintf>|/sprintf FORMAT, LIST>,
+because it's really more like -268.99999999999994315658 instead.
+Similarly, C<int "Info"> produces Inf, see
+L<perldata/Special floating point: infinity (Inf) and not-a-number (NaN)>
+for explanation.  Usually, the L<C<sprintf>|/sprintf FORMAT, LIST>,
 L<C<printf>|/printf FILEHANDLE FORMAT, LIST>, or the
 L<C<POSIX::floor>|POSIX/C<floor>> and L<C<POSIX::ceil>|POSIX/C<ceil>>
 functions will serve you better than will L<C<int>|/int EXPR>.