Why my local bundle is not loading?

I have put my local bundle (Demo.zip) under /src folder. Although I've defined Plugin class inside this bundle, it is not loading. No error or nothing. I'm expecting a new Content Element in Backend, if it is working.

I'm using Contao 4.5.6

Inside the main /composer.json, I've added.

Code:

---

...
    "autoload": {
        "psr-4": { "": "src/" },
    },
...

---

Do I've to create class ContaoManagerPlugin inside /app folder and load the bundle from there, which I am trying to avoid. My understanding is that if I've defined a Plugin class inside my bundle, then it will get loaded by the contao-manager.

Can you tell me where am I missing? Thanks