cal: improve util-linux page and split POSIX, osx and *BSD (#12172)

Co-authored-by: Juri Dispan <juri.dispan@posteo.net>
Co-authored-by: Sebastiaan Speck <12570668+sebastiaanspeck@users.noreply.github.com>

pages/linux/cal.md

@@ -1,16 +1,24 @@
 # cal
 
-> Prints calendar information, with the current day highlighted.
+> Display a calendar with the current day highlighted.
 > More information: <https://manned.org/cal>.
 
 - Display a calendar for the current month:
 
 `cal`
 
-- Display previous, current and next month:
+- Display [3] months spanning the date:
 
 `cal -3`
 
+- Display the whole calendar for the current [y]ear:
+
+`cal --year`
+
+- Display the next twelve months:
+
+`cal --twelve`
+
 - Use Monday as the first day of the week:
 
 `cal --monday`