add logo at homepage, add forum in issue template (#161)

.github/ISSUE_TEMPLATE/config.yml

+blank_issues_enabled: true
+contact_links:
+  - name: "😊 Discussions"
+    url: https://github.com/hpcaitech/ColossalAI/discussions
+    about: Ask questions and discuss with other Colossal-AI community members in our forum

README.md

 # Colossal-AI
-
+![logo](./docs/images/Colossal-AI_logo.png)
+<div align="center">
+   <h3> <a href="https://arxiv.org/abs/2110.14883"> Paper </a> | <a href="https://www.colossalai.org/"> Documentation </a> | <a href="https://github.com/hpcaitech/ColossalAI/discussions"> Forum </a> | <a href="https://medium.com/@hpcaitech"> Blog </a></h3>
+</div>
 An integrated large-scale model training system with efficient parallelization techniques.
 
-Paper: [Colossal-AI: A Unified Deep Learning System For Large-Scale Parallel Training](https://arxiv.org/abs/2110.14883)
-
-Blog: [Colossal-AI: A Unified Deep Learning System For Large-Scale Parallel Training](https://www.hpcaitech.com/blog)
-
 ## Installation
 
 ### PyPI
@@ -34,10 +33,6 @@ Install and enable CUDA kernel fusion (compulsory installation when using fused
 pip install -v --no-cache-dir --global-option="--cuda_ext" .
 ```
 
-## Documentation
-
-- [Documentation](https://www.colossalai.org/)
-
 
 ## Use Docker
 
@@ -82,7 +77,7 @@ model = ...
 # sampler by default
 train_dataset = ... 
 train_dataloader = get_dataloader(dataset=dataset,
-                                shuffle=True,
+                                shuffle=True
                                 )