Cannot setup example_light

I think the example configuration for example_light still uses an old identifier:

https://github.com/home-assistant/example-custom-config/blame/master/custom_components/example_light/README.md#L18

should be:

- platform: example_light

I this is correct, I can create an PR but even with this change, I can't get it to work. in the logs I see this:

```
Unable to install package awesomelights==1.2.3: ERROR: Could not find a version that satisfies the requirement awesomelights==1.2.3 (from versions: none) ERROR: No matching distribution found for awesomelights==1.2.3 WARNING: You are using pip version 19.3; however, version 19.3.1 is available. You should consider upgrading via the 'pip install --upgrade pip' command.
1:21 util/package.py (ERROR) - message first occurred at 1:19 and shows up 2 times
Platform error: light - Requirements for example_light not found: ['awesomelights==1.2.3'].
1:19 config.py (ERROR)
You are using a custom integration for example_light which has not been tested by Home Assistant. This component might cause stability problems, be sure to disable it if you do experience issues with Home Assistant.
1:19 loader.py (WARNING)
```

Start with custom_components/example_light/README.md at the linked configuration example and inspect how example_light declares its requirements. Reproduce the setup error involving awesomelights==1.2.3, then verify the platform identifier and dependency behavior; done means the documented configuration is current and the example can be set up successfully.

Written by the indexing model from the issue text.