Lightning network should be Bitcoin Lightning Network and explained

[riccardobl]

To simplify things for newcomers, in the fliers, i think Lightning Network should be renamed to Bitcoin Lightning Network (since there are and can be technically more Lightning Networks (ie. the ltc one..)) and it should use the same icon of Bitcoin Network with the bolt overlayed on top, to make it clear that it is still bitcoin and not something else. Additionally, if we can somehow find space for another section, we should explain in short the LN.