diff --git a/README b/README
index b0bb6fc67d..5d1b375e64 100644
--- a/README
+++ b/README
@@ -158,6 +158,14 @@ and only if the version number in the development branch indicates that it
 contains development code (i.e. a "snapshot" version, according to
 `version-to-list`).
 
+If there is no upstream (:url is nil), the presence of :release-branch
+just indicates that release and devel branches in elpa.git are desired
+(the name given in :release-branch is ignored). The release branch is
+named `externals-release/<pkg-name>' for GNU ELPA and
+`elpa-release/<pkg-name>` for NonGNU ELPA. The standard package branch
+externals/<pkg-name> is the devel branch in GNU ELPA; the standard
+branch elpa/<pkg-name> is the devel branch in non-GNU ELPA.
+
 ** =:ignored-files FILES=
 Names of files or directories that should not be included in the tarballs.