update the blinkt readme with info on systemd services (#505)

Co-authored-by: Steve Karg <skarg@users.sourceforge.net>

apps/blinkt/README.md

@@ -12,15 +12,82 @@ and run the daemon at powerup (and immediately):
     $ sudo systemctl enable pigpiod
     $ sudo systemctl start pigpiod
 
-## Building
+## WiFi Power
+
+If you are using a Raspberry Pi with WiFi, you will likely want 
+to disable WiFi Power saving.  Under Raspberry Pi OS, so the following.
+
+### Startup service in systemd
+
+To manage to start programs you should use systemd Unit files. 
+
+File name: /etc/systemd/system/wlan0pwr.service
+
+You can edit the file using the systemd edit:
+
+    rpi ~$ sudo systemctl --full --force edit wlan0pwr.service
+
+In the empty editor insert these statements, save them and quit the editor:
+
+    [Unit]
+    Description=Disable wlan0 powersave
+    After=network-online.target
+    Wants=network-online.target
+
+    [Service]
+    Type=oneshot
+    ExecStart=/sbin/iw wlan0 set power_save off
+
+    [Install]
+    WantedBy=multi-user.target
+
+Enable the new service with:
+
+    rpi ~$ sudo systemctl enable wlan0pwr.service
+    
+## Building the Blinkt! BACnet Application
     
 Build from the root folder:
 
     $ make blinkt
 
-## Running
+## Running the Blinkt! BACnet Application
 
 Run from the bin/ folder:
 
     $ ./bin/bacblinkt 9009
 
+## Blinkt! as a Startup service with systemd
+
+To manage to start programs you should use systemd Unit files. 
+Here is a very simple template you can use to start to solve your problem. 
+Create a new service with:
+
+    rpi ~$ sudo systemctl --full --force edit bacnet.service
+
+In the empty editor insert these statements, save them and quit the editor:
+
+    [Unit]
+    Description=BACnet Service
+    After=network-online.target
+
+    [Service]
+    ExecStart=/home/pi/bacnet.sh
+
+    [Install]
+    WantedBy=network-online.target
+
+Enable the new service after the next reboot with:
+
+    rpi ~$ sudo systemctl enable bacnet.service
+
+Create your bacnet.sh shell script in your home folder (change from pi if 
+that is not your home folder).  Use the shell script to set any environment
+variables that you want, or configuration settings for the bin/bacblinkt 
+application such as a specific device ID.
+
+A simplistic bacnet.sh script will look like this (with stdout/stderr to /dev/null):
+
+    #!/bin/bash
+    /home/pi/bacnet-stack/bin/bacblinkt 9009 > /dev/null 2>&1
+