Reload guard.yaml without losing the bounties

systemctl reload guard, guard reload or SIGHUP reads the configuration
again: a watch keeps its bounties and counts under the same name and
takes its new settings at once; its source starts again only if it
changed; watches gone stop, new ones start; a file with a mistake is
refused. The Housecarl connection, state, socket and log wait for a
restart, and guard reload says so.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -49,6 +49,8 @@ watch:
 * **IPv6 by /64**, as the ban list says: one customer usually has a
   whole /64 and moves around in it.
 * **Housecarl away?** Bans wait and are sent once it answers.
+* **`systemctl reload guard`** puts a changed guard.yaml to work
+  without losing what Guard has counted.
 * **`guard test`** shows what a watch's patterns find in a log, and whom
   they would ban, before you trust it.