Update installation instructions.

README.md

@@ -34,7 +34,11 @@ or just send me a patch.
 You will need `libpcap` installed.  Most OSX machines seem to have it.  All major Linux distributions have it available
 either by default or with a package like `libpcap-dev`.
 
-Clone the repo somehow, probably like this:
+The easiest way to get `node_pcap` and its tools is with `npm`:
+
+    npm install pcap
+
+If you want to hack on the source code, you can get it from github.  Clone the repo like this:
 
     git clone git://github.com/mranney/node_pcap.git