docs(previousprime) correct grammar

subjects/previousprime/README.md

@@ -2,9 +2,9 @@
 
 ### Instructions
 
-Write a **function** which returns the first prime number which is equal or inferior to the `u64` passed as parameter.
+Create a **function** which returns the first prime number which is less than or equal to the `u64` passed as an argument.
 
-If there are no primes inferior to the `u64` passed as parameter the function should return `0`.
+If there are no smaller primes, the function should return `0`.
 
 ### Expected function