docs: fix 'Invalid filename' issue in 'Fast Start' guide

[abiriadev]

Please refer to #63.

Changes

• Instruct users to copy the SQL script before running sqlcmd.
• Use docker compose cp instead of docker cp to avoid needing a container ID.
• Remove unnecessary shell access instructions(exec -it bash).

I suggest updating the PDF guide to mirror these changes for consistency. Unfortunately, I'm unsure how to update it. If there's something that I can do, please let me know.

Regards.