[gnome-backgrounds] README: extend guidelines to supplemental

[Jakub Steiner <jimmac src gnome org>]

commit 6dfbb20479e57902a53d28f090bd2ba35a287869
Author: Jakub Steiner <jimmac gmail com>
Date:   Thu Jun 18 12:24:45 2020 +0200

    README: extend guidelines to supplemental
    
    Addresses some aspects of https://gitlab.gnome.org/GNOME/gnome-backgrounds/-/issues/7

 README.md      |  13 ++++++++++++-
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---
diff --git a/README.md b/README.md
index 61c8b85..97d9d98 100644
--- a/README.md
+++ b/README.md
@@ -14,10 +14,21 @@ The default wallpaper has historically been strictly abstract, low contrast and
 
 It is desirable to have a wide mix of themes and colors for the additional wallpapers. Photographs and 
illustrations that would otherwise be too contrasty and with high frequency detail to be a good backdrop are 
perfectly suitable. Photos should generally be at least 3840x2160px, with no artifacts such as chromatic 
aberation. Generally 16:9 aspect ratio is preferred as the wallpapers get scaled with the `background-size: 
cover` equivalent method and wide displays are becoming more and more common.
 
-### Low Fidelity and Size Constraints
+#### Cultural Considerations
+
+GNOME is deployed globally. Be aware of some bad connotations in certain geographical areas. Depictions of 
some animals, flags or body parts are better avoided.
+
+#### Low Fidelity and Size Constraints
 
 One wallpaper is reserved for plain color to be used for remote access where it's benefitial for the 
compression algorith to cope with it with ease. Unfortunately due to distribution limits, the background 
collection has to keep its size contrained to around 40MB. This forces us to replace assets rather than add 
them. You can download the [Nostalgia](https://flathub.org/apps/details/im.bernard.Nostalgia) app to view 
previous release wallpapers.
 
+#### Sharpness
+
+Many photographic sources look great as a thumbnail or scaled down, but at 1:1 aren't 100% sharp. While it 
may not present itself as a problem on an average laptop screen, the wallpaper has to work at super wide 
screens where it's cropped to fit and is presented at 1:1 in many cases. Many otherwise suitable background 
images just fall short when observed at the nominal pixel view.
+
+![Bad Scaling](badscaling.jpg)
+
+
 ## License
 
 CCBYSA / Public Domain / CC0 is preferred. All attribution goes to the AUTHORS file.
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