docs: next.js instructions (#898)

Fixed next.config.js example to a working version per this:
#860 (comment)

Co-authored-by: Jari Mustonen <jari@itsellesi.fi>

website/pages/docs/next.mdx

@@ -44,7 +44,7 @@ module.exports = {
       {
         test: /\.svg$/i,
         issuer: /\.[jt]sx?$/,
-        resourceQuery: { not: /url/ }, // exclude if *.svg?url
+        resourceQuery: { not: [...fileLoaderRule.resourceQuery.not, /url/] }, // exclude if *.svg?url
         use: ['@svgr/webpack'],
       },
     )