diff --git a/vendor/double-conversion/UPDATING.md b/vendor/double-conversion/UPDATING.md
index 8a7e4bc8570..55f4b49574a 100644
--- a/vendor/double-conversion/UPDATING.md
+++ b/vendor/double-conversion/UPDATING.md
@@ -1,7 +1,7 @@
 © 2016 and later: Unicode, Inc. and others.
 License & terms of use: http://www.unicode.org/copyright.html
 
-## Updating double-conversion from Github to ICU4C
+## Updating double-conversion from Github to Vendor
 
 Go to https://github.com/google/double-conversion/releases/latest/ to determine the latest version number; for the examples below, suppose it is `v3.0.0`.
 
@@ -9,4 +9,12 @@ Run `pull-from-upstream.sh` as below:
 
 	./pull-from-upstream.sh v3.0.0
 
-Further instructions coming soon
+## Updating double-conversion from Vendor to ICU4C
+
+The relevant files from double-conversion are copied (svn cp) from Vendor to icu4c/source/i18n.  In order to integrate changes from a new version of double-conversion, the changes in Vendor after updating from Github should be merged into their corresponding copies in ICU4C.
+
+Instructions on how to do this should be written by the first person who performs such an update.
+
+For reference, the original commit including all of the svn copies is here:
+
+http://bugs.icu-project.org/trac/changeset/40929