Add check that article contains "figure" instead of MarkDown image

[georgik]

Hugo performs optimization of resources and it might add gray tint to image.
This increases a processing time.

Example:

![Export Camera photo](./img/camera.webp "Export Camera photo")

Correct format should be:

{{< figure
    default=true
    src="img/camera.webp"
    caption="Export Camera photo"
    >}}

Please, add check and update the Contribution Guide.