CO_2 in README

README.md

@@ -10,7 +10,7 @@ The room should be ventilated as soon as one LED turns red.
 
 The *CO<sub>2</sub> Ampel* can:
 
-* Display CO2 concentration on LED ring.
+* Display CO<sub>2</sub> concentration on LED ring.
 * Allow calibration.
 * Get current time over [NTP](https://en.wikipedia.org/wiki/Network_Time_Protocol)
 * Send data over [MQTT](https://en.wikipedia.org/wiki/MQTT).
@@ -76,7 +76,7 @@ In Arduino IDE *Serial Monitor* or PlatformIO *Monitor*, type `help` + <kbd>Ente
 * `calibrate` (Starts calibration process).
 * `calibrate 600` (Starts calibration process, to given ppm).
 * `calibrate! 600` (Calibrates right now, to given ppm).
-* `co2 1500` (Sets co2 level, for debugging purposes).
+* `co2 1500` (Sets CO<sub>2</sub> level, for debugging purposes).
 * `color 0xFF0015` (Shows color, specified as RGB, for debugging).
 * `csv 60` (Sets CSV writing interval, in s).
 * `format_filesystem` (Deletes the whole filesystem).