Clarify that the repo SHA-1 has changed

Change-Id: I3bda5abdabf04676b3bc651146df7ca983fc7126
diff --git a/src/source/downloading.md b/src/source/downloading.md
index 40e881b..b3a5f1c 100644
--- a/src/source/downloading.md
+++ b/src/source/downloading.md
@@ -35,6 +35,10 @@
  - For version 1.16, the SHA-1 checksum for repo is
  19ba8290344752da23e00cfb2b26afb43b463fe6
 
+ - *Note: an incorrect SHA-1 checksum had been published
+ for repo version 1.16. That version of repo was not
+ harmful, but it pointed to the wrong back-end server.*
+
 
 ## Initializing a Repo client ##