Document -1 as the value that disables roll_keep

[Socialpranker]

Fixes caddyserver/caddy#7863

Summary

The roll_keep docs say to set the value to 0 to disable the retention limit, but that's not what the code does: modules/logging/filewriter.go treats a RollKeep of 0 as "not set" and falls back to the default of 10 (filewriter.go#L258-L260). The value that actually removes the limit is -1, which the underlying rotator (lumberjack) treats as "no limit" for any MaxBackups <= 0.

A maintainer confirmed this in the issue thread and noted the fix belongs here (in the docs), not in a behavior change to caddy itself.

Change

One-line correction to the roll_keep description: documents -1 as the disabling value and explains that 0 falls back to the default of 10 instead of disabling anything.

Test plan

• Read the corrected sentence against filewriter.go's actual RollKeep/MaxBackups handling to confirm the new wording matches behavior.
• This is a documentation-only change with no code or build output to run.

[Socialpranker]

Friendly ping — this is a one-line docs fix that's been open since 10 July.

The roll_keep docs say 0 disables the retention limit, but filewriter.go treats 0 as "not set" and falls back to the default of 10; -1 is the value that actually disables it (caddyserver/caddy#7863, still open).

Should be a quick one whenever someone has a moment.

[Socialpranker]

Still here a few weeks on — it's a one-liner, so happy to tweak the wording if the phrasing isn't right, just say so.

[Socialpranker]

Heads up for whoever gets to this: #566 opened a duplicate fix for the same issue (caddyserver/caddy#7863) on 8/15. Functionally near-identical (both correct the disable value to -1), but this PR's wording also clarifies that 0 isn't a no-op — it falls back to the default of 10 — which #566's doesn't mention. Leaving it to you to pick whichever you'd rather merge; happy to close this one if you'd prefer to take #566 instead.