docs(readme): Updated readme file

Author: dev-xero

README.md

@@ -2,3 +2,14 @@
 Grep is a command-line utility in Unix and Unix-like operating systems used for searching and manipulating text or regular expressions within files. The name "grep" stands for `Global Regular Expression Print`.
 
 This implementation is part of the exercise in chapter 11 of the 'Rust Programming Language' book.
+
+## Usage
+The program accepts two arguments:  
+1. The string to search for, and
+2. The file to search in
+
+As an example,  
+```sh
+cargo run -- body poem.txt > output.txt
+```
+Will search for the string `body` in `poem.txt` and write the lines containing that string to output.txt.