[BIP-4] Build a Litecoin Tunnel

This proposal seeks to: Add a Litecoin tunnel in BoringDAO's ecosystem. The primary motivating factor for this proposal is that Litecoin always has been considered as Bitcoin’s experimental substitution. Litecoin also has a very large community, so build a new Litecoin tunnel is beneficial for Boring community.

According to the design in the whitepaper, before activating a new tunnel, the community needs to pledge at least 3000 BOR.