feat(www): add link to rule source on GitHub (denoland#1264)

By following this link users can learn how the rule is implemented,
and discover details about corner cases.

Also it eases potential contributions, if something needs to be fixed
or improved about the current rule.

www/routes/rules/[name].tsx

@@ -1,3 +1,5 @@
+import IconBrandGithub from "https://deno.land/x/[email protected]/tsx/brand-github.tsx";
+
 import jsonData from "../../static/docs.json" with { type: "json" };
 
 import { Handlers, PageProps } from "$fresh/server.ts";
@@ -26,6 +28,9 @@ export const handler: Handlers<RuleData> = {
 
 export default function RulePage(props: PageProps) {
   const rule: RuleData = props.data;
+  const ruleSlug = rule.code.replaceAll("-", "_");
+  const sourceLink =
+    `https://github.com/denoland/deno_lint/blob/main/src/rules/${ruleSlug}.rs`;
 
   return (
     <div>
@@ -42,6 +47,15 @@ export default function RulePage(props: PageProps) {
       <main>
         <Rule rule={rule} open />
       </main>
+      <footer>
+        <a class="hover:underline" href={sourceLink}>
+          <IconBrandGithub
+            title="View rule source on GitHub"
+            class="w-5 h-5 mr-1 inline"
+          />
+          Rule source
+        </a>
+      </footer>
     </div>
   );
 }