Use --home instead of HOME=, to reduce confusion

Using-systemd-units-instead-of-cron.md

@@ -8,9 +8,8 @@ After=network-online.target
 
 [Service]
 Type=oneshot
-# Directory where the acme.sh script resides.
-Environment="HOME=/path/to/"
-ExecStart=/path/to/acme.sh <your acme.sh arguments here>
+# --home's argument should be where the acme.sh script resides.
+ExecStart=/path/to/acme.sh --home /path/to <your acme.sh arguments here>
 # acme.sh returns 2 when renewal is skipped (i.e. certs up to date)
 SuccessExitStatus=0 2
 ```