Update README.md

[lalyos]

when using apko via docker, the provided samples fail with the following error:

$ docker run -v "$PWD":/work cgr.dev/chainguard/apko build examples/alpine-base.yaml apko-alpine:test apko-alpine.tar

ℹ️            | loading config file: alpine-base.yaml
⚠️            | remote configurations are an experimental feature and subject to change.
Error: failed to load image configuration: unable to fetch remote include from git: failed to parse git reference alpine-base.yaml: not enough path data available
2023/11/06 13:01:35 error during command execution: failed to load image configuration: unable to fetch remote include from git: failed to parse git reference alpine-base.yaml: not enough path data available

The reson is that the cgr.dev/chainguard/apko image has no workdir specified:

docker inspect cgr.dev/chainguard/apko | jq .[0].Config.WorkingDir
""

therefore the default working directory is the root "/".

workarounds:

• all path should be absolute, like: /work/examples/alpine-base.yaml (unconvenient)
• specify WORKDIR for the official apko image: this would be the nicest solution i'm not sure if you have any objections against that
• use --workdir or -w to specify the workdir at runtime

Right now the the 3 option is the quickest.