improve descriptions

Author: smdn

examples/ATtinyX02/BasicUsage/BasicUsage.ino

@@ -3,7 +3,7 @@
 #include <Arduino.h>
 #include <MHZ19X.h>
 
-// use PA6 is used for RX and PA7 for TX.
+// This code uses serial communication with PA6 as RX and PA7 as TX to connect to the MH-Z19C.
 auto co2sensor = MHZ19C<PIN_PA6, PIN_PA7>();
 
 void setup()

examples/ESP32/BasicUsage/BasicUsage.ino

@@ -3,11 +3,13 @@
 #include <Arduino.h>
 #include <MHZ19X.h>
 
-// use UART2 (Hardware serial; RX=GPIO16, TX=GPIO17)
+// This code uses the UART2 serial port to connect to the MH-Z19C.
+// (Hardware serial; RX=GPIO16, TX=GPIO17)
 auto co2sensor = MHZ19C_UART2();
 
 /*
-// use UART1 (Hardware serial; RX=GPIO9, TX=GPIO10)
+// This code uses the UART1 serial port to connect to the MH-Z19C.
+// (Hardware serial; RX=GPIO9, TX=GPIO10)
 auto co2sensor = MHZ19C_UART1();
 */