cmd: Add build-info command; update CertMagic

cmd/commands.go

@@ -188,6 +188,12 @@ config file; otherwise the default is assumed.`,
 		}(),
 	})
 
+	RegisterCommand(Command{
+		Name:  "build-info",
+		Func:  cmdBuildInfo,
+		Short: "Prints information about this build",
+	})
+
 	RegisterCommand(Command{
 		Name:  "environ",
 		Func:  cmdEnviron,