Added how to run the program in the readme

Usage: puissance4 <mode> <row> <col>
    mode  specifies the mode:
        1 = single player game (random),
        2 = single player game (AI),
        3 = two players game
row   specifies the number of rows (>= 4)
col   specifies the number of columns (>= 4)

README.md

@@ -23,3 +23,16 @@ Use this command to clean the project.
 
 Use this command to compile and start the tests.
 
+## Run the project
+
+Execute the `puissance4` file.
+
+```
+Usage: puissance4 <mode> <row> <col>
+    mode  specifies the mode:
+        1 = single player game (random),
+        2 = single player game (AI),
+        3 = two players game
+row   specifies the number of rows (>= 4)
+col   specifies the number of columns (>= 4)
+```