Update collection-index.yml (#48)

You did amazing work on this ecosystem! I'm doing my best to spread this convention and I hope it will get the traction it deserves🙂
In this collection, I plan to add some missing DevOps-focused features, and more in the future 
Currently, it has Pulumi (which is a prominent alternative to terraform)

Author: danielbraun89

_data/collection-index.yml

@@ -33,3 +33,8 @@
   contact: https://github.com/mpriscella/features/issues
   repository: https://github.com/mpriscella/features
   ociReference: ghcr.io/mpriscella/features
+- name: DevContainers-Contrib Features
+  maintainer: Daniel Braun
+  contact: https://github.com/devcontainers-contrib/features/issues
+  repository: https://github.com/devcontainers-contrib/features
+  ociReference: ghcr.io/devcontainers-contrib/features