[Documentation] add a simple Hello World example Component

[distante]

Describe the problem you have/What new integration you would like
I find that the ESPHome contributing documentation is missing crucial information for it to allow new people to create External Components or to contribute to the main Repo with new Official Components.

The documentation is focusing too much on "how it should be" ratter than "how it is done", of course we can check how other components work (and even the documentation it self says that), but there are A LOT of components. If one never ever saw the source code of an Component, then it could be really frustrating.

Please describe your use case for this integration and alternatives you've tried:

• Not an integration

Additional context

While I have not that much experience with Python and C++, I have a lot of experience with another languages and work as a full time developer. I am not the best, but for sure not the worst. The last days I a was trying to create a PoC for a Ventilation controller using UART that I wanted to create in the hopes to be able to share with the community. The environment setup was kind of easy, but then (I feel like) I wasted too much time just navigating code to find out things like "how to inject a GPIO into my config" or "How to link a button component?" (this last one still gives me errors).

As I understood until now, there are some rules the code python generation functions, or parameter names need to follow that are not shown anywhere. (Side note, this is probably known by someone that knows the code generation library?).

I know there is a lot of living code to keep everything up-to-date in the documentation, but I propose the creation of a simple Hello World custom component, that can, for example, read the voltage of an GPIO, show it on a Text Sensor and do something when a Button is clicked and it should be part of the documentation.

I really believe that something like this would let more people that have not much time start contributing.

Happy Holidays!