(website) Changed email link style to generate constant html with harp.

Currently, I use harp.js to generate website, but it generates several patterns for email link.
URL is encoded but every time it changes (unicode and ascii are mixed?), and it causes redundant commits.
As a workaround, I changed <> style to []() style.

Author: ksoichiro

README.md

@@ -78,7 +78,7 @@ Please check the [FAQ](docs/faq.md) and [contributing guideline](https://github.
 
 ## Developed By
 
-* Soichiro Kashima - <soichiro.kashima@gmail.com>
+* Soichiro Kashima - [soichiro.kashima@gmail.com](mailto:soichiro.kashima@gmail.com)
 
 
 ## Thanks