[postr] Fix links in README.md

[Germán Poo-Caamaño <gpoo src gnome org>]

commit d6c166fc9db062234a214e55bb0b40f4a5c7ded3
Author: Germán Poo-Caamaño <gpoo calcifer org>
Date:   Wed May 30 14:37:22 2018 +0000

    Fix links in README.md

 README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/README.md b/README.md
index 0f5c836..5a6aad1 100644
--- a/README.md
+++ b/README.md
@@ -14,5 +14,5 @@ use but exposing enough of Flickr to be useful.
 
 Postr requires PyGObject and GTK+3.
 
-[postr-logo]: 
+[postr-logo]: data/48x48/postr.png
 [1]: https://flickr.com/