could use more detail about NVMe overprovisioning

[shribe]

The sections Overprovisioning by secure erase and partition table trick](https://openzfs.github.io/openzfs-docs/Performance%20and%20Tuning/Workload%20Tuning.html#id61) & NVMe overprovisioning could use a bit more explanation, or a link to external information.

I am unclear as to why installing an NVMe, creating partitions for SLOG and/or L2ARC which sum to significantly less than the NVMe size would not be sufficient.

[gmelikov]

I agree, we can add some info about SSD FTL layer, NAND erase block sizes and reason why somebody wants to have free space on disk.