Instructions on how to build Docker image

[tiagostutz]

Is your feature request related to a problem? Please describe.

I struggled building a NextJS Docker image because the provided Docker image doesn't have the COPY --from=builder /app/next-i18next.config.js ./ instruction. So I had problems with Initial locale argument was not passed into serverSideTranslations and next-i18next was unable to find a user config

Describe the solution you'd like

There could be in the README instructions a section "Deploying with Docker" that has the instructions on how to put the config file in the build process

Describe alternatives you've considered

This could be:

## Deployment Tips
When building your Docker image following NextJS instructions, please remember to:
- uncomment the line `COPY --from=builder /app/next.config.js ./`
- add the following line right above that: `COPY --from=builder /app/next-i18next.config.js ./`

Additional context

N/A

[isaachinman]

Of course, when building in Docker, you'll need to copy next-i18next.config.js just like all other source files. If you feel mentioning this is relevant, feel free to open a PR to update the documentation.

[fangyibkk]

Encounter the same problem and found this really help. Thanks a lot, I will create the PR.