Add github star history

README.md

@@ -87,6 +87,9 @@ $ leadtime stat --owner=nao1215 --repo=gup --markdown
 
 ## Contributing / Contact
 First off, thanks for taking the time to contribute! heart Contributions are not only related to development. For example, GitHub Star motivates me to develop!
+
+[![Star History Chart](https://api.star-history.com/svg?repos=nao1215/leadtime&type=Date)](https://star-history.com/#nao1215/leadtime&Date)
+
 
 If you would like to send comments such as "find a bug" or "request for additional features" to the developer, please use one of the following contacts.
 - [GitHub Issue](https://github.com/nao1215/leadtime/issues)