Link to Bitlegal.io for legal status around the globe

We currently only link to a few US-centric guidances [in the FAQ](https://bitcoin.org/en/faq#is-bitcoin-legal) (and we have to keep this content up to date, even though we are not lawyers).

BitLegal provides detailed and up-to-date information on the evolving legal environment for a large number of countries, with links to official statements, and they seem to do a good job at this thus far. So we could just delegate this to a specialized resource.