Create a project scope

[fulldecent]

Creating a scope to define what contributions this project is looking to accept will help the community to close other issue.

Here is an example of something I think is clearly out of scope:

https://github.com/google/open-location-code/issues/428

But I can't convince anybody else of this unless 1) someone with commits access here says so, or 2) I can point to the project scope.

[fulldecent]

Recommended tag: project organization

[fulldecent]

The project scope should include:

• New implementations will be considered only as a pull request with a full working implementation that passes all test cases and works with our continuous integration, not an issue.

This will allow to close issues like this: https://github.com/google/open-location-code/issues/428 as out of scope.