docs: add stargazers over time

Author: jellydn

README.md

@@ -333,4 +333,8 @@ Thanks goes to these wonderful people ([emoji key](https://allcontributors.org/d
 
 <!-- ALL-CONTRIBUTORS-LIST:END -->
 
-This project follows the [all-contributors](https://github.com/all-contributors/all-contributors) specification. Contributions of any kind welcome!
+This project follows the [all-contributors](https://github.com/all-contributors/all-contributors) specification. Contributions of any kind are welcome!
+
+### Stargazers over time
+
+[![Stargazers over time](https://starchart.cc/CopilotC-Nvim/CopilotChat.nvim.svg)](https://starchart.cc/CopilotC-Nvim/CopilotChat.nvim)