Say in --help where the database is and what each report prints (closes #177)

The help of sfdupes and of scan names the database, its default path
and SFDUPES_DATABASE. The help of report and trees lists the columns,
the order of the rows and the four escapes. The help of info lists its
lines. The help of dwim says that it scans /, should run as root and
keeps the scan in the database.

The README's opening drops its sentence on copies deleted after the
scan, an edge case that its report and trees sections already cover.

Model: opus-5-5

TODO.md

@@ -29,6 +29,11 @@
 Newest first. An entry ends with its date and its issue or branch, where those
 are known.
 
+- The help of `sfdupes` and of `scan` names the database, its default path and
+  `SFDUPES_DATABASE`. The help of `report` and `trees` lists the columns, the
+  order of the rows and the escapes. The help of `info` lists its lines. The
+  help of `dwim` says that it scans `/`, should run as root and keeps the scan
+  in the database (2026-11-11, https://git.eeqj.de/sneak/sfdupes/issues/177)
 - New `scan` flag `--exclude PATH`, which may be repeated. The walk neither
   enters nor records an excluded path, and keeps the records below it. An
   operand at or below one is a fatal error (2026-11-11,