Add Contribution and Ownership Information to README

[ian-bunner]

l2l is a young library with great potential. To accelerate it's growth we need a strong community of users who are willing to positively contribute. With that in mind, we should create a section detailing how l2l users can contribute. Ideally this section would cover both the mechanics of contributing and what contributions we are most looking for.

Additionally, we should add a section listing the code owners.

[seba-1511]

Done, in the form of the citation information.