check_http - handle empty response

docs/20_Checks/check_http.md

@@ -47,7 +47,8 @@ PARAMETERS:
   Define request:
   -u URL           Set url to fetch; eg. https://www.example.com/
   -m METHOD        Set a method, eg. HEAD; default: GET
-  -c PARAMS        additional curl params
+  -c PARAMS        additional curl params; curl will be executed 
+                   with '[PARAMS] -si -X [METHOD] --connect-timeout 10 [URL]'
 
   What to check:
   -s STATUSCODE    exact Statuscode to check; 3 digits; by default critical