Added documentation for log level influencing signals for cf-serverd

Ticket: CFE-4413
Changelog: None

reference/components/cf-serverd.markdown

@@ -22,6 +22,8 @@ affected by `common` and `server` control bodies.
 * This daemon reloads it's config when the SIGHUP signal is received.
 * If `enable_report_dumps` exists in `WORKDIR` (`/var/cfengine/enable_report_dumps`) `cf-serverd` will log reports provided to `cf-hub` to `WORKDIR/diagnostics/report_dump` (`/var/cfengine/diagnostics/report_dumps`). This data is useful when troubleshooting reporting issues with CFEngine Enterprise.
 * `cf-serverd` always considers the class ```server``` to be defined.
+* `SIGUSR1` sets the log level to debug.
+* `SIGUSR2` sets the log level to notice.
 
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