First cut a Docker devsite/build image.
Ignore the currently-active Dockerfile.
Encoding fix in the code_block plugin.
Expose and publish the "jekyll serve" port.
locales isn't necessary, after all.
Pass explicit --source and --destination arguments.
Autoopen on Macs.
Gate image building behind an option.
Shave those yaks.
Shave those yaks in script/preview.
Use jekyll's multiple config files.
Separate image building from running.
Use a non-root user for the build.
Write READMEs for the docker/ and build/ dirs.
Use descriptive paths within devsite/build.

This will make that README less of a lie.
Add a section to the README about script/preview.
Include documentation in the top-level README.
Add script/build to do a one-off build.
Add a mention in the docs.
Stop the script on first error.