fish: add battery function

fish/functions/battery.fish

@@ -0,0 +1,15 @@
+function battery
+	# Only works on Mac
+	if test (uname -s) != Darwin
+		echo "Unsupported OS: "(uname -s)
+		return 1
+	end
+
+	set --local battery_status (pmset -g batt | string split0)
+	set --local battery_charge (echo $battery_status | rg --only-matching "\d+%")
+	set --local power_source   (echo $battery_status | rg --only-matching  "[A-Za-z]+\sPower")
+
+	set_color green
+	echo "⚡️ Running on $power_source with $battery_charge charge"
+	set_color normal
+end