Doc and make it slightly better

TODO.markdown

@@ -11,6 +11,7 @@ things that need to be fixed.
 * Speed
 * SaltLength in NSEC3 is ugly to set, should be automatically done. There are prolly a few more
     settings just like that -- need to look at them.
+    -edns NSID is another
 
 ## Examples to add
 

edns.go

@@ -129,7 +129,12 @@ func (rr *RR_OPT) SetDo() {
 
 // Nsid returns the NSID as hex character string.
 func (rr *RR_OPT) Nsid() string {
-	return "NSID: " + rr.Option[0].Data
+        for i := 0; i < len(rr.Option); i++ {
+                if rr.Option[i].Code == OptionCodeNSID {
+	                return "NSID: " + rr.Option[i].Data
+                }
+        }
+        return "Not found"
 }
 
 // SetNsid sets the NSID from a hex character string.