Add -h for the check command

Because even I don't remember what it can do anymore.

lib/msf/ui/console/module_command_dispatcher.rb

@@ -122,6 +122,11 @@ module ModuleCommandDispatcher
   # Checks to see if a target is vulnerable.
   #
   def cmd_check(*args)
+    if args.first =~ /^\-h$/i
+      cmd_check_help
+      return
+    end
+
     ip_range_arg = args.shift || mod.datastore['RHOSTS'] || framework.datastore['RHOSTS'] || ''
     opt = Msf::OptAddressRange.new('RHOSTS')
 
@@ -162,6 +167,32 @@ module ModuleCommandDispatcher
     end
   end
 
+  def cmd_check_help
+    print_line('Usage: check [option] [IP Range]')
+    print_line
+    print_line('Options:')
+    print_line('-h  You are looking at it.')
+    print_line
+    print_line('Examples:')
+    print_line('')
+    print_line('Normally, if a RHOST is already specified, you can just run check.')
+    print_line('But here are different ways to use the command:')
+    print_line
+    print_line('Against a single host:')
+    print_line('check 192.168.1.123')
+    print_line
+    print_line('Against a range of IPs:')
+    print_line('check 192.168.1.1-192.168.1.254')
+    print_line
+    print_line('Against a range of IPs loaded from a file:')
+    print_line('check file:///tmp/ip_list.txt')
+    print_line
+    print_line('Multi-threaded checks:')
+    print_line('1. set THREADS 10')
+    print_line('2. check')
+    print_line
+  end
+
   def report_vuln(instance)
     framework.db.report_vuln(
       workspace: instance.workspace,