[DOCS] faq - docker image size

[lmeyerov]

When running docker load -i containers.tar.gz, sometimes admins will see an error like:

Errors processing tar file (exit status 1): open ....: no space left on device

Show how to:

• Diagnose: Check docker images, data root location & current size, ...
• Fix: Change data root, clear out old images
• Put in FAQ that links to dedicated configuration or maintenance page