readme: add disambiguation links for other go link services

Signed-off-by: Will Norris <[email protected]>

Author: willnorris

README.md

@@ -5,6 +5,8 @@
 golink is a private shortlink service for your [tailnet].
 It lets you create short, memorable links for the websites you and your team use most.
 If you're new to golink, learn more in our [announcement blog post](https://tailscale.com/blog/golink/).
+If you were looking for a SaaS go link service that doesn't use Tailscale,
+you might be thinking of [golinks.io](https://golinks.io) or [trot.to](http://trot.to)
 
 [tailnet]: https://tailscale.com/kb/1136/tailnet/