[retro-gtk] Add .gitignore

[Adrien Plazas <aplazas src gnome org>]

commit 95497f6e1164e9ef52638ad4d6a8a45a849b76f4
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Sun Nov 5 08:26:55 2017 +0100

    Add .gitignore

 .gitignore |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..9e80904
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+build
+.flatpak-builder