Some touch-ups in the attach reference and man-page;
- remove uses of old images (ubuntu 14.04)
- adds some more wording about `-i` and `-t` to use the detach sequence.
- use `--filter` instead of `grep` to list the container, to make the
example more portable.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
74086bc93b