README: add 'flyctl'

README.md

@@ -14,6 +14,7 @@ $ staticd <tool>
 - `bat`: [sharkdp/bat][bat], a cat(1) clone with wings.
 - `btm`: [ClementTsang/bottom][btm], yet another cross-platform graphical process/system monitor.
 - `cloudflared`: [cloudflare/cloudflared][cloudflared], Argo Tunnel client.
+- `flyctl`: [superfly/flyctl][flyctl], command line tools for fly.io services
 - `k9s`: [derailed/k9s][k9s], Kubernetes CLI to manage your clusters in style.
 - `upx`: [upx/upx][upx], the Ultimate Packer for eXecutables.
 - `xh`: [ducaale/xh][xh], friendly and fast tool for sending HTTP requests.
@@ -22,6 +23,7 @@ $ staticd <tool>
 [bat]: https://github.com/sharkdp/bat
 [btm]: https://github.com/ClementTsang/bottom
 [cloudflared]: https://github.com/cloudflare/cloudflared
+[flyctl]: https://github.com/superfly/flyctl
 [k9s]: https://github.com/derailed/k9s
 [upx]: https://github.com/upx/upx
 [xh]: https://github.com/ducaale/xh