[gnome-software.wiki] Add stub carousel tile section

[Philip Withnall <pwithnall src gnome org>]

commit 875c9749d507796bf4b1e2738942695b5aa85460
Author: Philip Withnall <philip tecnocode co uk>
Date:   Thu Sep 9 14:31:20 2021 +0000

    Add stub carousel tile section

 Software-metadata.md | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
---
diff --git a/Software-metadata.md b/Software-metadata.md
index aa2e7db..b03f402 100644
--- a/Software-metadata.md
+++ b/Software-metadata.md
@@ -94,6 +94,16 @@ You can improve the links:
 
 <br clear="both"/>
 
+Carousel tile <a name="carousel-tile"></a>
+---
+
+TODO
+
+You can improve the carousel tile:
+ * [How to set the carousel tile background 
colour](#user-content-how-to-set-the-carousel-tile-background-colour)
+
+<br clear="both"/>
+
 Where metadata comes from
 ===
 
@@ -137,4 +147,10 @@ How to fix incorrect safety and permissions information
 ---
 
  - https://docs.flatpak.org/en/latest/sandbox-permissions.html
+ - TODO
+
+How to set the carousel tile background colour
+---
+
+ - 
https://gitlab.gnome.org/GNOME/gnome-software/-/blob/eac007a8bf87207347ab2c8baf629d5d58aa0c6b/lib/gs-app.c#L4239-4248
  - TODO
\ No newline at end of file