message: Update README.md: goal
diff: HugeCTR is a high-efficiency GPU framework designed for Click-Through-Rate (CTR) estimation training.
  Design Goals:
  -* Optimized for recommender system
  -* Easy to be customized
  +* Fast: it's a speed-of-light CTR training framework;
  +* Dedicated: we consider every thing you need in CTR training;
  +* Easy: you can start your work now, no matter you are a data scientist, a learner, or a developer.
  Please find more introductions in our [**HugeCTR User Guide**](docs/hugectr_user_guide.md) and doxygen files in directory `docs\`
  