check-routeros-update: split off check-perpetual-license...

... and also add documentations, screenshot, etc.

check-perpetual-license.rsc

@@ -65,7 +65,7 @@
   }
 
   :if ([ :typeof $SentCertificateNotification ] = "str" && \
-       [ :totime ($License->"deadline-at") ] - 3w > [ :timestamp ]) do={
+       [ :totime ($License->"deadline-at") ] - 4w > [ :timestamp ]) do={
     $LogPrint info $ScriptName ("Your license was successfully renewed.");
     $SendNotification2 ({ origin=$ScriptName; \
       subject=([ $SymbolForNotification "white-heavy-check-mark" ] . "License renewed"); \