chore: update the gnokey quickstart link (#4222)

This pull request updates the gnokey quickstart link, as the previous
one is no longer valid.

---------

Co-authored-by: Leon Hudak <33522493+leohhhn@users.noreply.github.com>
Co-authored-by: Manfred Touron <94029+moul@users.noreply.github.com>

Author: 3 people

gno.land/cmd/gnokey/README.md

@@ -8,4 +8,4 @@
     $> cd ./gno
     $> make install_gnokey
 
-Also, see the [quickstart guide](https://github.com/gnolang/gno/blob/master/examples/gno.land/r/demo/boards/README.md).
+Also, see the [quickstart guide](../../../docs/users/interact-with-gnokey.md).