//In woocomerce.php file
//find this function get_woocommerce_currency_symbol()


// Add you currency and symbol as another "case statement" in "switch statement"

case 'INR' : $currency_symbol = 'Rs'; break;

//Another change in admin/admin-settings.php

// Add below lone in "Currency Array"

'INR' => __( 'Indian Rupee', 'woothemes' ),