Add 'Known Limitations' page or section

[HenrikBengtsson]

Add "Known Limitations" to help clarify what's possible and not possible, and give suggestions for workarounds. This helps newcomers and helps to communicate the design decisions behind Wynton.

Examples:

• No backup
• Compute nodes have no internet access
• Compute nodes have no dev tools
• No SSH access to compute nodes
• No interactive jobs
• Dev nodes have limited web access via proxy
• Login and xfer nodes don't have environment modules
• No Docker and Apptainers limitations in building containers locally
• ...