phrase notification more intuitively

mixing % full and bytes free in one sentence is confusing

7% full - 1.8GB/2.0GB (free/total)

The meaning of the usage number (free) is further away from
the actual number.

7% full - 0.2GB/2.0GB (used/total)

reads more intuitively

Author: teleivo

slack/slack.go

@@ -56,7 +56,7 @@ func formatMessage(r usage.Report, host string) []slack.Block {
 	var sb strings.Builder
 	for _, l := range r.Limits {
 		perc := uint64((float64(l.Used) / float64(l.Total)) * 100)
-		fmt.Fprintf(&sb, "• %q - *%d%% full* - %s/%s (free/total)\n", l.Path, perc, humanize.Bytes(l.Free), humanize.Bytes(l.Total))
+		fmt.Fprintf(&sb, "• %q - *%d%% full* - %s/%s (used/total)\n", l.Path, perc, humanize.Bytes(l.Used), humanize.Bytes(l.Total))
 	}
 	limits := slack.NewTextBlockObject("mrkdwn", sb.String(), false, false)
 	limitSection := slack.NewContextBlock("limits", limitHeader, limits)

slack/testdata/slack-message.snapshot

@@ -20,7 +20,7 @@
 				},
 				{
 					"type": "mrkdwn",
-					"text": "• \"/mnt/volume1\" - *50% full* - 2.5 GB/5.0 GB (free/total)\n• \"/mnt/volume2\" - *90% full* - 500 MB/5.0 GB (free/total)\n"
+					"text": "• \"/mnt/volume1\" - *50% full* - 2.5 GB/5.0 GB (used/total)\n• \"/mnt/volume2\" - *90% full* - 4.5 GB/5.0 GB (used/total)\n"
 				}
 			]
 		},