Fly auth docker (#4484)

* Update text styling and add note for token expiration

* test commit

* Fix trailing whitespace linting issue

Author: Lucais11

internal/command/auth/docker.go

@@ -22,10 +22,11 @@ import (
 
 func newDocker() *cobra.Command {
 	const (
-		long = `Adds registry.fly.io to the docker daemon's authenticated
-registries. This allows you to push images directly to fly from
-the docker cli.
-`
+		long = `Adds registry.fly.io to the Docker daemon's authenticated
+registries. This allows you to push images directly to Fly.io from
+the Docker CLI.
+
+Note: Tokens generated by this command expire after 5 minutes.`
 		short = "Authenticate docker"
 	)