config: document how to translate image config into runtime config

[philips]

There are several fields in the OCI Image Config that directly translate to a fields on the Runtime Config. We should document how those fields translate.

The obvious ones:

• User
• Env
• Entrypoint
• Cmd
• WorkingDir

UX ones (used to help users but not automatically mapped):

• ExposedPorts
• Volumes

Optional as they depend on the user and largely shouldn't be dictated by image author:

• Memory
• MemorySwap
• CPUShares

[philips]

As discussed @wking @stevvooe

[philips]

@cyphar could you take a swing at adding this language?

[wking]

See also #454, which would set the required runtime-spec config version.

[cyphar]

@philips Yeah, I'll give it a shot.

[cyphar]

I've done this in #492.

[RobDolinMS]

@philips Can this Issue be closed with active discussion now happening in PR #492 ?

[stevvooe]

@RobDolinMS We should really wait for the issue to get resolved before closing it.