Document and increase max running healing inserts: heal up to 250MiB …

[ArneBab]

…per download.

[ArneBab]

As a test I downloaded a 300MiB file with the new code. It triggered 2700 healing inserts, so the old limit would have only permitted healing 20% of the dead blocks.

[ArneBab]

@desyncr does your :+1: mean you reviewed this?

[desyncr]

@ArneBab Yeah, code looks OK 👍