add bit more help to exec node

Point out that parameters with spaces should be quoted

nodes/core/core/75-exec.html

@@ -45,6 +45,7 @@
     <p>By default uses exec() which calls the command, then gets a callback on completion, returning the complete result in one message, along with any errors.</p>
     <p>Optionally can use spawn() instead, which returns the output from stdout and stderr as the command runs (usually one line at a time). On completion it then returns a return code (on the 3rd output).</p>
     <p>The optional append gets added to the command after the <b>msg.payload</b> - so you can do things like pipe the result to another command.</p>
+    <p>Parameters with spaces should be enclosed in quotes - <i>"This is a single parameter"</i></p>
     <p>If stdout is binary a <i>buffer</i> is returned - otherwise returns a <i>string</i>.</p>
 </script>