[example] fix community doc (#3586)

Adjusted the style of Community Examples to be consistent with other titles

examples/community/README.md

-#Community Examples
+## Community Examples
 
 Community-driven Examples is an initiative that allows users to share their own examples to the Colossal-AI community, fostering a sense of community and making it easy for others to access and benefit from shared work. The primary goal with community-driven examples is to have a community-maintained collection of diverse and exotic functionalities built on top of the Colossal-AI package.