docs(net-diag) help + name

@jbenet @whyrusleeping

Docs read net-diag. It seems the command was previously registered as
diag. Which do you prefer?

core/commands2/diag.go

@@ -28,6 +28,14 @@ type DiagnosticOutput struct {
 }
 
 var diagCmd = &cmds.Command{
+	// TODO UsageLine: "net-diag",
+	// TODO Short:     "Generate a diagnostics report",
+	Help: `ipfs net-diag - Generate a diagnostics report.
+
+	Sends out a message to each node in the network recursively
+	requesting a listing of data about them including number of
+	connected peers and latencies between them.
+`,
 	Run: func(res cmds.Response, req cmds.Request) {
 		n := req.Context().Node
 

core/commands2/root.go

@@ -62,7 +62,7 @@ var rootSubcommands = map[string]*cmds.Command{
 	"name":      nameCmd,
 	"add":       addCmd,
 	"log":       logCmd,
-	"diag":      diagCmd,
+	"net-diag":  diagCmd,
 	"pin":       pinCmd,
 	"unpin":     unpinCmd,
 	"version":   versionCmd,