feat: mention sshackd dep and link to repo in README

README.md

@@ -7,8 +7,10 @@ This expiration means access to Sparkbox Slack is required to get SSH access to
 
 ## How to use
 
+Note: You'll need a running instance of [`sshackd`](https://github.com/sparkbox/sshackd) somewhere for this to work at all. Pass your instance URL with the `-u` flag.
+
 1. Download `sb` from the latest release for your architecture.
 2. Login by running `sb login`. This should launch a Sign-in with Slack prompt in your browser. Paste the resultant ID and token back to `sb`.
-3. You're now set to generate a SSH Certificate, run `sb ssh`.
+3. You're now set to generate a SSH Certificate, run `sb ssh -u your.sshackd.instance`.
 4. Verify your local `ssh-agent` has the cert by running `ssh-add -l`and noting the `ECDSA-CERT` entry.
 5. You can now SSH to any host that is configured to trust the Certificate Authority.

cmd/ssh.go

@@ -180,7 +180,7 @@ func getCert(url string) (cert Cert, error error) {
 
 func init() {
 	rootCmd.AddCommand(sshCmd)
-	sshCmd.Flags().StringP("url", "u", "https://slackd-beta.herokuapp.com", "Set an alternate API URL")
+	sshCmd.Flags().StringP("url", "u", "https://sshackd.herokuapp.com", "Set an alternate API URL")
 	sshCmd.Flags().BoolP("print", "p", false, "Print cert and private key instead of adding to ssh-agent")
 	sshCmd.Flags().BoolP("write", "w", false, "Write cert (key-cert.pub) and key (key) to files instead of adding them to ssh-agent")
 }