Update README.md

README.md

 # Projet_Q4_Groupe_O4
 
+
+prerequise: 
+
+- gcc
+- make 
+
+To launch the program: 
+
+- download the project
+- open the project directory with terminal
+- Enter the following commands:
+    make fact
+    ./ fact your_input_filename your_output_filename
+
+The output file will appear in the project file directory.
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