[docs] Add sponsor button

docs/assets/docsify-init.js

@@ -13,6 +13,7 @@ const linksMenu = '<div class="links-menu">' +
   '<a href="https://github.com/imgproxy" target="_blank" title="GitHub"><img src="/assets/github.svg" /></a>' +
   '<a href="https://twitter.com/imgproxy_net" target="_blank" title="Twitter"><img src="/assets/twitter.svg" /></a>' +
   '<a href="https://discord.gg/5GgpXgtC9u" target="_blank" title="Discord"><img src="/assets/discord.svg" /></a>' +
+  '<a href="https://github.com/sponsors/imgproxy" target="_blank" title="Sponsor"><img src="/assets/heart.svg" /></a>' +
   '</div>';
 
 const docEditBase = 'https://github.com/imgproxy/imgproxy/edit/master/docs/';

docs/assets/heart.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><!--! Font Awesome Pro 6.4.2 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license (Commercial License) Copyright 2023 Fonticons, Inc. --><path fill="#fff" d="M47.6 300.4L228.3 469.1c7.5 7 17.4 10.9 27.7 10.9s20.2-3.9 27.7-10.9L464.4 300.4c30.4-28.3 47.6-68 47.6-109.5v-5.8c0-69.9-50.5-129.5-119.4-141C347 36.5 300.6 51.4 268 84L256 96 244 84c-32.6-32.6-79-47.5-124.6-39.9C50.5 55.6 0 115.2 0 185.1v5.8c0 41.5 17.2 81.2 47.6 109.5z"/></svg>