Add git GUI - Meld (#2034)

Add Meld to the GUI page: https://meldmerge.org

Author: olfek

data/guis/meldmerge.yml

@@ -0,0 +1,11 @@
+---
+name: "Meld"
+project_url: "https://meldmerge.org"
+image_tag: "images/guis/meldmerge.png"
+platforms:
+  - "Linux"
+  - "Windows"
+price: "Free"
+license: "GPLv2 or later"
+order: 29
+---