docs: clarify installation docs a bit more

README.md

@@ -8,7 +8,10 @@ This expiration means access to Sparkbox Slack is required to get SSH access to
 ## How to use
 
 1. Download `sb` from the [latest release](https://github.com/sparkbox/sb/releases) for your architecture.
-1. Run the file to install `sb`. *On a Mac, you will need to `control + click` the unzipped file and select "Open" from the menu.*
+1. Unzip the file.
+1. *On a Mac, you will need to `control + click` the unzipped binary and select "Open" from the menu.*
+1. Move the `sb` binary to a location your `$PATH` understands: e.g. `mv sb /usr/local/bin/sb`
+1. Start a fresh shell instance (new Terminal window)
 1. 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`.
 1. You're now set to generate a SSH Certificate, run `sb ssh`.
 1. Verify your local `ssh-agent` has the cert by running `ssh-add -l`and noting the `ECDSA-CERT` entry.