Readme uncertainty (for Solidus\Rails beginners)

[czepesch]

Hi there! Firstly I apologize if Issues is not right place for that. If so point me a right direction and close this issue.

My problem is, as Rails\Solidus beginner I don't fully understand how to customize this extension.

1. Set the logo path preference to include your store / company logo. - I placed it in spree.rb (is it right place?), logo now in invoice, but it is huge, covering all page (sizing not working).
2. Add your own own footer texts to the locale. - is it myapp/config/locales/en.yml? I placed some content there but can't see any changes in invoice
3. Override any of the partial templates. - how can I do this? I've created /app/views/spree/admin/orders/_header.pdf.prawn and changed fill_color to another color, can't see any changes in the header color.

and so on.. I would be grateful for any hints on how and where to do customization.