Update README.md

- Added clarification about composer type of magento-core
- Our Magento-Team would offer itself as a support contact. ==> Added "brandung" to the list
- I, Amir, (or brandung) would love to be enlisted as a core contributor to show some dedication to this project. ==> Added Amir Tchavoshinia to the contributors list
Merge pull request #101 from bragento/patch-1

Update README.md