add picfit to gin user list (#1661)

agreed with the project's author.
cc @thoas
thanks!

README.md

@@ -2001,3 +2001,4 @@ Awesome project lists using [Gin](https://github.com/gin-gonic/gin) web framewor
 * [fnproject](https://github.com/fnproject/fn): The container native, cloud agnostic serverless platform.
 * [photoprism](https://github.com/photoprism/photoprism): Personal photo management powered by Go and Google TensorFlow.
 * [krakend](https://github.com/devopsfaith/krakend): Ultra performant API Gateway with middlewares.
+* [picfit](https://github.com/thoas/picfit): An image resizing server written in Go.