Adding known issue of etc/docker/certs documentation.

[abbytiz]

@cftorres @aaron-prindle @nkubala

[abbytiz]

fixes #21

[aaron-prindle]

LGTM

[duggelz]

rm -rf /etc/docker? This sounds like something important? What exactly am I wiping out?

$ sudo ls -al /etc/docker
total 24
drwx------   2 root root  4096 Sep  8  2015 .
drwxr-xr-x 186 root root 16384 Aug 18 16:10 ..
-rw-------   1 root root   281 Sep  8  2015 key.json

$ sudo cat /etc/docker/key.json
{
    "crv": "P-256",
    "d": "long string off stuff",
    "kid": "long string of stuff",
    "kty": "EC",
    "x": "long string of stuff",
    "y": "long string of stuff"
}

[nkubala]

Hmm, I wonder if we could get away with doing something like sudo chmod -R 755 /etc/docker? @aaron-prindle @dlorenc @duggelz WDYT