fix links to containerignore doc

[Pvlerick]

What type of PR is this?

/kind documentation

What this PR does / why we need it:

Documentation

How to verify it

N/A

Which issue(s) this PR fixes:

None

Special notes for your reviewer:

In the selection of the ignore file, the logic is wrong; the comment here https://github.com/containers/buildah/blob/main/pkg/parse/parse.go#L1290 says that .containerignore will be preferend but the code obviously does the opposite since the .dockerignore is checked for in the second if.

Proving test: https://github.com/Pvlerick/buildah/blob/container-ignore-file-priority/pkg/parse/parse_test.go#L233

However, changing this logic is a breaking change, and this [file].dockerignore/[file].containerignore is not documented (at least I didn't find any mention of it)

Does this PR introduce a user-facing change?

NO

[flouthoc]

This appears to be a path on quick look maybe make it .containerignore or .dockerignore. Anyways is there any need to include .dockerignore in this heading ? I think the text below describes talks about .dockerignore.

[flouthoc]

One nit above otherwise PR LGTM

[TomSweeneyRedHat]

LGTM once the nit is cleansed.

[Pvlerick]

Suggestion applied.

FYI, I aligned it with what I could find here: https://github.com/containers/podman/blob/main/docs/source/markdown/podman-build.1.md.in#L635

[Pvlerick]

BTW no comment on the ignore files priorities discrepancies between the doc and the code ? :-)

[rhatdan]

/approve
LGTM

[flouthoc]

LGTM
/lgtm
/approve

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: flouthoc, Pvlerick, rhatdan

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