README file update

[Zenaan Harkness]

The screen README has the following:

---
screen -r [pid.tty.host|tty.host]
  Reattach to a specific detached session. The terminal emulator
  reconfigures according to your $TERMCAP or $TERM settings.
  When you have multiple screens detached, you must supply the session
  name.
---

>From my testing, I think the first line should read at least:

screen -r [pid.tty.host|tty.host|tty]

since it worked for me - perhaps it doesn't always work??

cheers
zen