Make README more descriptive

Author: new2code

README.md

@@ -1,2 +1,38 @@
-# python-factorial
+# Python factorial
+
 A short Python program that finds the factorial of a positive integer.
+
+## Setup and run
+
+### Prerequisites
+
+Before you can run this program, you need to [install Python](https://www.python.org/downloads/) on your system.
+
+### Cloning the repository
+
+To clone this repository locally, run the following command from your terminal:
+
+```shell copy
+git clone https://github.com/new2code/python-factorial.git
+```
+
+### Running the program
+
+1. To open the repository's directory, run the following command from your terminal:
+
+    ```shell copy
+    cd python-factorial
+    ```
+
+2. To calculate the factorial of a specific number, in `factorial_finder.py`, update the value of `number`.
+3. To run the program on Mac or Linux, run the following command in your terminal:
+
+    ```shell copy
+    python factorial.py
+    ```
+
+    Otherwise, to run the program on Windows, run the following command from the command line:
+
+    ```shell copy
+    py factorial.py
+    ```