pkg/server: doc that fileInfo.name is a base name

For the DownloadHandler, this change alleviates confusion about whether
the name from the fileInfo should be cleaned out of slashes and such
before being zip archived.

Change-Id: I3ccbd760a2c08787d4ee4e22d8dc8ed066d2f82f

pkg/server/download.go

@@ -67,7 +67,7 @@ type DownloadHandler struct {
 
 type fileInfo struct {
 	mime    string
-	name    string
+	name    string // base name of the file
 	size    int64
 	modtime time.Time
 	rs      io.ReadSeeker