docs: added acknowledgements

Author: ken-matsui

docs/acknowledgements.md

@@ -0,0 +1,15 @@
+## Acknowledgements
+
+This project exists thanks to all the people who contribute.
+
+<a href="https://github.com/poac-dev/poac/graphs/contributors">
+  <img src="https://contributors-img.web.app/image?repo=poac-dev/poac" />
+</a>
+
+<a href="https://star-history.com/#poac-dev/poac&Date">
+ <picture>
+   <source media="(prefers-color-scheme: dark)" srcset="https://api.star-history.com/svg?repos=poac-dev/poac&type=Date&theme=dark" />
+   <source media="(prefers-color-scheme: light)" srcset="https://api.star-history.com/svg?repos=poac-dev/poac&type=Date" />
+   <img alt="Star History Chart" src="https://api.star-history.com/svg?repos=poac-dev/poac&type=Date" />
+ </picture>
+</a>