cmd/cue: more references to docs for --with-context

[rogpeppe]

What version of CUE are you using (cue version)?

$ cue version
cue version v0.0.0-20221118123638-79dbd92b3e4f

      -buildmode exe
       -compiler gc
     CGO_ENABLED 1
          GOARCH amd64
            GOOS linux
         GOAMD64 v1
             vcs git
    vcs.revision 79dbd92b3e4f5cbfc69bfdd27f954b4c582a56ff
        vcs.time 2022-11-18T12:36:38Z
    vcs.modified false

Does this issue reproduce with the latest release?

Yes

What did you do?

cue help import

What did you expect to see?

Some reference to where to find the docs for the -l and --with-context flags.

What did you see instead?

Some usage of both of the above flags, but no hint as to where to find the docs for them.

It's clear from #2124 that even some experienced CUE developers can't easily find those docs (I count myself as one of their number) so surfacing them more explicitly should help with that.

[jpluscplusm]

@rogpeppe @myitcv Can we move this to https://github.com/cue-lang/docs-and-content, or does it need to remain here to explicitly track changes to cue help ... output?

[myitcv]

This issue should remain open to sign-post people to cue help flags which is where --with-context is further detailed. The docs and content work can be done at the same time or separately. Thanks