docs: added how-to documentation for the PriceList API (#2260)

* docs: added price list how-to

* added links to price list conceptual docs

* added link to the how-to guide

* fixed typo in file extension

www/docs/sidebars.js

@@ -220,6 +220,10 @@ module.exports = {
               id: "advanced/backend/taxes/manual-calculation",
               label: "Calculate Taxes Manually"
             },
+            {
+              type: "doc",
+              id: "advanced/backend/price-lists/use-api"
+            },
           ]
         },
         {