fix #609 : [plugin] Update the README and the doc to mention potential credentials error when using the plugin.

[sebsto]

Description

Adds documentation for Docker credential store errors that users may encounter when running swift package archive --allow-network-connections docker.

Changes

• Added a note in readme.md explaining how to resolve Docker credential store errors
• Added a note in Sources/AWSLambdaRuntime/Docs.docc/Deployment.md with the same guidance

Problem

Users may encounter authentication errors when the Swift package plugin attempts to pull Docker images, particularly when Docker is configured with a credential store (e.g., docker-credential-desktop). This issue is documented in #609.

Solution

The documentation now provides two workarounds:

1. Remove the credsStore entry from ~/.docker/config.json
2. Use the --disable-sandbox flag with the archive command

Both notes link to issue #609 for additional context and discussion.

Related Issue

Fixes #609