Update system-info macOS user agent

Add CPU temperature to `status-info`, conditionally display battery
charge percentage, and documents the commands.

system-info/system-info-macOS.sh

@@ -12,11 +12,17 @@ fi
 trap '[ -f $cache_file ] && rm $cache_file; exit' INT
 trap '[ -f $cache_file ] && rm $cache_file; exit' TERM
 
+# Check if a battery is installed.
+if ioreg -w0 -l|grep BatteryInstalled &> /dev/null; then
+  has_battery=true
+else
+  has_battery=false
+fi
+
 while true; do
   # Get the current CPU temperature.
   cpu_temp="`/usr/local/bin/osx-cpu-temp`"
-  # Check if a battery is installed.
-  if ioreg -w0 -l|grep BatteryInstalled &> /dev/null; then
+  if $has_battery; then
     # Parse the current battery charge percentage.
     battery=" `pmset -g batt | grep --color=never -Eo '\d+%'` ↯"
   fi