Add organization repository proposal and plan docs

[brentvatne]

The documents in this pull request provide an answer and plan of action for the longstanding question posed in #176: "What packages belong in react-native-community?"

Part of the reason that this question remained unanswered for so long is that there wasn't any formal decision making process in place for the organization. The creators of the organization decided that a practical way to make good decisions for the organization would be to have representatives from each of the react-native partner organizations provide input and vote on any significant changes:

Members of the organizations listed as partners on the react-native repository collaborate to manage the React Native Community organization and related community tools, such as React Native Directory. Decisions that will meaningfully change the React Native Community organization require approval by a majority of partners.

The scope of responsibility and list of partners is expected to change over time, and will be documented here alongside other decisions and actions.

---

The primary intended audience for these documents is maintainers of repositories that exist inside of the react-native-community organization at the time of writing.

The secondary audience is the broader set of developers that use React Native to build their apps and may be curious about the motivations and decision making processes behind the changes that they will notice in the react-native-community organization.