Update README.md

On creating a new Okta object the readme just states to enter 'your-domain,' so I passed '<company>.okta.com' (the full subdomain).  Doing this causes the request in NetworkAbstraction to generate a hostname of <company>.okta.com.okta.com which causes Node to throw a very obscure SSL error on every request.  Updated readme to make this explicitly clear so other people don't make the same dumb mistake.