Add Description and relevant tags

[GreyEcologist]

Hey,
seeing a similar PR from Ezra, can we add a description to the repo, I think that description suggested by @orenyodfat should work:
Infra is the lowest daostack's stack layer. It provides generalized decision-making mechanisms for any use, DAO or otherwise.

Also, can we add some tags, i.e "DAO", "Ethereum" and "Blockchain"