io: clarify MultiReader documentation
Fixes #7216.
LGTM=minux.ma
R=golang-codereviews, minux.ma
CC=golang-codereviews
https://golang.org/cl/54740044
diff --git a/src/pkg/io/multi.go b/src/pkg/io/multi.go
index 2c7e816..ab8dd5d 100644
--- a/src/pkg/io/multi.go
+++ b/src/pkg/io/multi.go
@@ -26,7 +26,8 @@
// MultiReader returns a Reader that's the logical concatenation of
// the provided input readers. They're read sequentially. Once all
-// inputs are drained, Read will return EOF.
+// inputs have returned EOF, Read will return EOF. If any of the readers
+// return a non-nil, non-EOF error, Read will return that error.
func MultiReader(readers ...Reader) Reader {
return &multiReader{readers}
}
