added links for custom integration and kafka integration
added links for custom integration and kafka integration

volodymyr-babak/thingsboard.github.io,volodymyr-babak/thingsboard.github.io,volodymyr-babak/thingsboard.github.io,thingsboard/thingsboard.github.io,volodymyr-babak/thingsboard.github.io,thingsboard/thingsboard.github.io,thingsboard/thingsboard.github.io,thingsboard/thingsboard.github.io