Discussion on SDK design document template

[hendrikebbers]

We decided to create a documentation for the design of our SDKs to beter specify new features and changes. The Documentation should be generic and therefore can be used as a based for all our SDK (and the SDK TCK) to implement new features. We want to add all SDK maintainers, committers and contributors to the discussion on creating those documentations. Based on that @rwalworth and @SimiHunjan created a suggestion for a SDK design document template. For a better discussion we created a PR (#48) that can be used to directly comment on the template. We plan to have the discussion open for 2 weeks before we bring this back to the TCK and vote on creating a repository for the documentation.