minor doc updates

doc.go

@@ -4,4 +4,6 @@
 // The watchdog package is meant to be used as a binary only.
 // The git tag version describes the state of the binary,
 // not the state of the library. The API is not yet stable.
+//
+// See https://git.rootproject.org/root/watchdog.go for pre-built binaries.
 package watchdog