[doc] add star graph
## Roadmap
[Projects](https://github.com/pion/sfu/projects/1)
+## Project status
+[![Stargazers over time](https://starchart.cc/pion/sfu.svg)](https://starchart.cc/pion/sfu)
+
## How to use
### 1. install signal server and make key.pem|cert.pem
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