Add note explaining that CONVERT rules are processed after --build-context
substitutions but before containers-registries.conf substitutions. Also
update matchType default documentation to reflect WILDCARD being the default.
Addresses: https://github.com/containers/buildah/pull/6647#discussion_r2727811695
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Signed-off-by: Konstantin Vyatkin <tino@vtkn.io>
