Style and wording fixes

lab2/lab2_demo_btn_read/lab2_demo_btn_read.ino

-#define BTN_PIN 3
+#define BTN_PIN         3
 
 const int tickDelay = 100;
 
 void setup() 
 {
-  // Alustame jadaühenduse
+  // Seadistame jadaühenduse
   Serial.begin(9600);
 
-  // Määrame nupu sisendiks
+  // Seadistame surunupu sisendina
   pinMode(BTN_PIN, INPUT);
 }
 
@@ -21,4 +21,4 @@ void loop()
   Serial.println(btnState);
 
   delay(tickDelay);
-}
\ No newline at end of file
+}