add swagger documentation

api/s3.go

@@ -4,7 +4,12 @@ import (
 	"github.com/gin-gonic/gin"
 )
 
-// GET /api/s3
+// @Summary Get S3 buckets
+// @Description Get list of S3 buckets.
+// @Tags S3
+// @Produce  json
+// @Success 200 {array} string "List of S3 buckets"
+// @Router /api/s3 [get]
 func apiS3List(c *gin.Context) {
 	keys := []string{}
 	for k := range context.Config().S3PublishRoots {