docs(concat_string): rephrase usage and description

subjects/devops/concat_string/README.md

@@ -9,7 +9,7 @@ Create a file `concat_string.py` that contains a function `concat` which takes i
 
 ### Usage
 
-Here is an example of how to use the `concat` function:
+Here is an example of how to use the `concat` function in a `test.py` script:
 
 ```python
 import concat_string
@@ -18,13 +18,15 @@ string2 = "World"
 print(concat_string.concat(string1, string2))
 ```
 
-This will output:
+Below is the expected output:
+
+````
 
 ```console
 $ python3 test.py
-Hello World
+Hello, World
 $
-```
+````
 
 ### References