Add simple examples

[VincentMarmiesse]

Hi,
A lot of my everyday uses are not in the documentation, ie:

• how to add a product/customer/category attribute?
• how to get the current customer?

In summary, it would be nice to have some "real life" code snippets.

[JulienPradet]

Thank you for the great suggestions. It helps us know what's really useful for the readers.
We'll try to add those along the way.

[VincentMarmiesse]

Some other suggestions:

• How to change the favicon?
• How to set the images placeholder?