Add notice for adding "--project-directory" for custom Docker Commands

[flawnn]

Please add a notice to the docs that you are adding --project-directory to custom Docker Compose commands - I literally sat a whole day on this trying to figure out the error I was getting from Docker Compose because this was not written anywhere but in this issue only.

The next version will have a fix. Coolfiy will automatically add `--project-directory` to the custom commands (if it does not exists) to make sure the context is correct.

Originally posted by @andrasbacsai in #2338 (comment)