tools: add v10 to alternative version docs menu

PR-URL: https://github.com/nodejs/node/pull/20586
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

tools/doc/html.js

@@ -168,6 +168,7 @@ function altDocs(filename) {
   }
 
   const versions = [
+    { num: '10.x' },
     { num: '9.x' },
     { num: '8.x', lts: true },
     { num: '7.x' },