Adds shared volume

[JJ]

And documentation on how to use it.

These are very minor changes but add to usability.

[JJ]

(I know I have the privs to merge this, but maybe someone else wants to check it out)

[alexm]

I tried this on an older docker image and it works fine:

docker run -t -v `pwd`:/home/perl6 rakudo-star perl6 /home/perl6/ls.p6

Is the volume really needed?

[alexm]

What does mal mean here? It sounds like a typo, but I may be wrong.

[JJ]

totally typo. Should be map. Will fix that.

[JJ]

Volume is not really needed. It's just a convenient place to put scripts. You can create new volumes with -v all the time.

[tianon]

As I noted over in docker-library/official-images#2599, I'm having a hard time understanding what's added by having an explicit VOLUME instruction in the Dockerfile here -- if -v is used on the docker run line, a volume or bind mount is created already, and no pre-defined VOLUME is actually necessary.

[JJ]

No, not really. It's just a convention,

[tianon]

I think the description in docker-library/official-images#2437 (comment) is decent context on why this VOLUME doesn't seem terribly appropriate (and could actually be actively harmful to users, while the absence of the explicit VOLUME doesn't prevent anything that's newly documented here):

The general rule we follow is that you should have a volume for where the application stores data (so $SONARQUBE_HOME/data is uncontestably appropriate), but configuration is almost never appropriate in a volume (unless it's specifically managed by the application itself at runtime and never supplied/managed manually by users, or there is an easy way to override the default in the image).

The reason for this is that, once defined, Docker has no means of "UNVOLUME" -- thus, once a volume, always a volume.

[JJ]

OK, you have a point here.