update godoc
diff --git a/errors.go b/errors.go
index a31ca30..58996ba 100644
--- a/errors.go
+++ b/errors.go
@@ -51,6 +51,18 @@
// type Stacktrace interface {
// Stacktrace() []Frame
// }
+//
+// The Frame type represents a call site in the stacktrace. Frame supports
+// the fmt.Formatter interface that can be used for printing information about
+// the stacktrace of this error. For example:
+//
+// if err, ok := err.(Stacktrace); ok {
+// for _, f := range err.Stacktrace() {
+// fmt.Printf("%+s:%d", f)
+// }
+// }
+//
+// See the documentation for Frame.Format for more details.
package errors
import (
