.github: add missing link to tailscale.md in license template

The missing link can be seen in the rendered file at
https://github.com/tailscale/tailscale/blob/main/licenses/android.md

Updates #cleanup

Signed-off-by: Will Norris <will@tailscale.com>

Author: willnorris

.github/licenses.tmpl

@@ -11,6 +11,7 @@ The following open source dependencies are used to build the [Tailscale Android
 Client][].  See also the dependencies in the [Tailscale CLI][].
 
 [Tailscale Android Client]: https://github.com/tailscale/tailscale-android
+[Tailscale CLI]: ./tailscale.md
 
 ## Go Packages