Updated docs to show that nmap module must be explicitly loaded

doc/scapy/installation.rst

@@ -164,6 +164,7 @@ Here are the topics involved and some examples that you can use to try if your i
 
   .. code-block:: python 
   
+     >>> load_module("nmap")
      >>> nmap_fp("192.168.0.1")
      Begin emission:
      Finished to send 8 packets.

doc/scapy/usage.rst

@@ -23,7 +23,7 @@ administrator privileges::
 
 If you do not have all optional packages installed, Scapy will inform you that 
 some features will not be available:: 
-
+                                 
     INFO: Can't import python gnuplot wrapper . Won't be able to plot.
     INFO: Can't import PyX. Won't be able to use psdump() or pdfdump().
 
@@ -1489,11 +1489,15 @@ Once we obtain a reasonable number of responses we can start analyzing collected
 nmap_fp
 ^^^^^^^
 
-If you have nmap installed you can use it's active os fingerprinting database with Scapy. First make sure that version 1 of signature database is located in the path specified by::
+Nmap fingerprinting (the old "1st generation" one that was done by Nmap up to v4.20) is supported in Scapy. In Scapy v2 you have to load an extension module first::
+
+    >>> load_module("nmap")
+
+If you have Nmap installed you can use it's active os fingerprinting database with Scapy. Make sure that version 1 of signature database is located in the path specified by::
 
     >>> conf.nmap_base
 
-Scapy includes a built-in ``nmap_fp()`` function which implements same probes as in Nmap's OS Detection engine::
+Then you can use the ``nmap_fp()`` function which implements same probes as in Nmap's OS Detection engine::
 
     >>> nmap_fp("192.168.1.1",oport=443,cport=1)
     Begin emission: