Add cfw:org-create-file-source to list of commands

Also show how to use it in README.

modules/app/calendar/README.org

@@ -34,7 +34,8 @@ calendar data from:
   (cfw:open-calendar-buffer
    :contents-sources
    (list
-    (cfw:org-create-source "Green")  ; orgmode source
+    (cfw:org-create-source "Green")  ; org-agenda source
+    (cfw:org-create-file-source "cal" "/path/to/cal.org" "Cyan")  ; other org source
     (cfw:howm-create-source "Blue")  ; howm source
     (cfw:cal-create-source "Orange") ; diary source
     (cfw:ical-create-source "Moon" "~/moon.ics" "Gray")  ; ICS source1

modules/app/calendar/config.el

@@ -33,6 +33,7 @@
 (use-package! calfw-org
   :commands (cfw:open-org-calendar
              cfw:org-create-source
+             cfw:org-create-file-source
              cfw:open-org-calendar-withkevin
              my-open-calendar))