Hi,

You can inherit the website_sale.product as follows in your custom module,

<template id="product_add_to_wishlist" inherit_id="website_sale.product" customize_show="True" 
          name="Wishlist Button" priority="20">
    <xpath expr="//div[@id='product_option_block']" position="inside">
    </xpath>
</template>

In the inherit_id you have to specify the id of the record that you need to inherit and apply the changes in the view using the xpath expression.

See a sample in the website_sale_wishlist module inheriting the same template.

<template id="product_add_to_wishlist" inherit_id="website_sale.product" customize_show="True" name="Wishlist Button" priority="20">
    <xpath expr="//div[@id='product_option_block']" position="inside">
        <t t-set="product_variant" t-value="product_variant or product._create_first_product_variant()"/>
        <t t-set="in_wish" t-value="product_variant and product_variant._is_in_wishlist()"/>
        <button t-if="product_variant" type="button" role="button" class="btn btn-link mt16 o_add_wishlist_dyn" t-att-disabled='in_wish or None' t-att-data-product-template-id="product.id" t-att-data-product-product-id="product_variant.id" data-action="o_wishlist"><span class="fa fa-heart" role="img" aria-label="Add to wishlist"></span> Add to wishlist</button>
    </xpath>
</template>

As you are new into the odoo development, it is not recommended to edit inside the odoo source code, always try to customize by creating a custom module in odoo community, if you are using the enterprise you can use the studio tool also.

For Reference: Odoo Website Development Tutorials

Thanks