clarify debug levels in the -h output

pd/src/s_main.c

@@ -435,8 +435,12 @@ static char *(usagemessage[]) = {
 "-font-weight <name>-- specify default font weight (normal or bold)\n",
 "-verbose         -- extra printout on startup and when searching for files\n",
 "-version         -- don't run Pd; just print out which version it is \n",
-"-d <n>           -- specify debug type: 1=out, 2=in, 4=linenumbers\n",
-"                      (combine by adding. e.g. -d 5 is -d 1 and -d 4)\n",
+"-d <n>           -- specify debug type:\n",
+"                    1=Pd->GUI\n",
+"                    2=GUI->Pd\n",
+"                    3=Pd->GUI and GUI->Pd\n",
+"                    5=Pd->GUI with Pd linenumbers\n",
+"                    7=Pd->GUI and GUI->Pd with Pd linenumbers\n", 
 "-noloadbang      -- suppress all loadbangs\n",
 "-stderr          -- send printout to standard error instead of GUI\n",
 "-nogui           -- suppress starting the GUI\n",