Stop the docs saying the migration does not work

Two places told an operator that `run` is unimplemented and refuses: the
usage text, and the first line of the README's status. Both predate `run`
being wired up, and the README contradicted itself three lines later, where
the command table says it works. Anyone reading either would conclude the
tool cannot migrate.

The rest of that section had drifted too: staging exists as a package, and
the package table was missing it along with applyplan, while the line counts
had aged. Recounted, and the column now says what it is measuring.

`report` really is unimplemented, so the usage text now says so where it is
advertised.

cmd/stalwart-migrate/main.go

@@ -48,7 +48,7 @@ func usage() {
 commands:
   preflight   run read-only checks and print the migration plan
   rehearse    convert this instance's settings and report what will NOT carry over (read-only)
-  run         perform the migration (not implemented yet - refuses)
+  run         perform the migration (needs --yes and --recovery-point-confirmed)
   status      show the state of an in-progress or completed run
-  report      print the validation report for a run`)
+  report      print the validation report for a run (not implemented yet)`)
 }