Note caveat with detaching using key sequence

[jcrben]

This has come up a few times, for example:

• https://stackoverflow.com/questions/19688314/how-do-you-attach-and-detach-from-dockers-process#comment40262294_19689048
• Detaching from a container in Mac OS X moby/moby#20864
• Unable to detach from container moby/moby#35491
• Debian Host: CTRL + P + Q doesn't keep container alive moby/moby#20227 (comment)
• https://forums.docker.com/t/ctrl-p-ctrl-q-does-not-detach/40273

- What I did
N/A
- How I did it
N/A
- How to verify it
N/A
- Description for the changelog
Update documentation of docker attach to note caveat with detaching using key sequence.

- A picture of a cute animal (not mandatory but encouraged)

(from https://commons.wikimedia.org/wiki/File:Beagle_puppy_Cadet_2.jpg)

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "patch-1" git@github.com:jcrben/cli.git somewhere
$ cd somewhere
$ git commit --amend -s --no-edit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[jcrben]

My commit is Github "Verified"; kinda surprised that isn't enough. I'll see about pulling it down.

I tested using -t and -i independently (with an image I had on hand, redis) and it didn't work - needed both and then it emitted read escape sequence and closed.

[codecov-io]

Codecov Report

Merging #1665 into master will not change coverage.
The diff coverage is n/a.

@@ Coverage Diff @@## master #1665 +/- ##
=======================================
Coverage 56.07% 56.07% =======================================
Files 306 306 Lines 20950 20950 =======================================
Hits 11747 11747 Misses 8354 8354 Partials 849 849

[thaJeztah]

My commit is Github "Verified"; kinda surprised that isn't enough. I'll see about pulling it down.

Yes, sorry about that; it's checking for a "DCO" sign-off (which is different than the commit being GPG-signed).

[thaJeztah]

LGTM

ping @vdemeester ptal

[silvin-lubecki]

LGTM 👍