docs(ispowerof2): make subject clearer

Add definition of power of 2

subjects/ispowerof2/README.md

@@ -2,7 +2,9 @@
 
 ### Instructions
 
-Write a program that determines if a given number is a power of 2.
+Write a program that determines if a given number is a power of 2. A number `n` is a power of 2 if it meets the following condition: $n = 2 ^ m$ where m is another integer number.
+
+For example, $4 = 2 ^ 2$ or $16 = 2 ^ 4$ are power of 2 numbers while 24 is not.
 
 This program must print `true` if the given number is a power of 2, otherwise it has to print `false`.
 
@@ -10,6 +12,8 @@ This program must print `true` if the given number is a power of 2, otherwise it
 
 - When there is only one argument, it will always be a positive valid `int`.
 
+
+
 ### Usage :
 
 ```console