Update "official repos" doc to mention 100 char short desc limit

The Hub no longer accepts short descriptions over 100 characters.

Signed-off-by: Andrew Page <admwiggin@gmail.com>

docs/sources/docker-hub/official_repos.md

@@ -60,7 +60,7 @@ should also:
 
 * Be named `README-short.txt`
 * Reside in the repo for the “latest” tag
-* Not exceed 200 characters
+* Not exceed 100 characters
 
 ### A logo