Add guidance on resizing NFS shares

[JimMadge]

✅ Checklist

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⤴️ Summary

• Add instructions to resize NFS shared
• Explain how a full home share can prevent users from logging in

🌂 Related issues

Closes #1402

🔬 Tests

• Worked through steps on existing SRE
• Built docs locally

[craddm]

LGTM