Add theme badge for hugo-coder (#513)

* Update README.md

Add theme budge for hugo-coder

* Update CONTRIBUTORS.md

Update contributors

CONTRIBUTORS.md

@@ -93,3 +93,4 @@
 - [Peter Duchnovsky](https://pduchnovsky.com)
 - [Alex Miranda](https://ammiranda.com)
 - [Alphonse Mariya](https://github.com/alfunx)
+- [Ziwei Pan])(https://github.com/PanZiwei/)

README.md

@@ -1,3 +1,5 @@
+[![Theme is hugo-coder](https://img.shields.io/badge/Theme-hugo--coder-2b8cbe)](https://github.com/luizdepra/hugo-coder)
+
 ![Hugo Coder Logotype](https://github.com/luizdepra/hugo-coder/blob/master/images/logos/logotype-a.png)
 
 A simple and clean blog theme for [Hugo](https://gohugo.io/).