esp8266/help: Add "sta_if.active(True)" command.

As reported on the forum by Roberthh.

esp8266/help.c

@@ -37,7 +37,7 @@ STATIC const char *help_text =
 "Basic WiFi configuration:\n"
 "\n"
 "import network\n"
-"sta_if = network.WLAN(network.STA_IF)\n"
+"sta_if = network.WLAN(network.STA_IF); sta_if.active(True)\n"
 "sta_if.scan()                             # Scan for available access points\n"
 "sta_if.connect(\"<AP_name>\", \"<password>\") # Connect to an AP\n"
 "sta_if.isconnected()                      # Check for successful connection\n"