docs: Add guide to showcase handling outputs

Add a guide which highlights how to handle action's outputs by writing
them to the client filesystem and using CUE's integrations to marshal
them as JSON.

Signed-off-by: Marcos Lilljedahl <marcosnils@gmail.com>

website/sidebars.js

@@ -53,6 +53,8 @@ module.exports = {
         "guides/custom-buildkit",
         "guides/self-signed-certificates",
         "guides/pushing-plan-dependencies",
+        "guides/coding-style",
+	"guides/handling-outputs",
       ],
     },
     {