[gnome-backgrounds] README additions

[Jakub Steiner <jimmac src gnome org>]

commit cc65412360155af9fcfcc91ac5a1c487847a3ef9
Author: Jakub Steiner <jimmac gmail com>
Date:   Thu Oct 8 14:02:28 2020 +0200

    README additions
    
    - cover the basics for wallpaper submissions
    
    Fixes https://gitlab.gnome.org/GNOME/gnome-backgrounds/-/issues/7

 README.md                   |  23 +++++++++++++++++++----
 backgrounds/Stripes.jpg     | Bin 7655884 -> 1552330 bytes
 backgrounds/Symbolics-1.png | Bin 1118282 -> 1686339 bytes
 3 files changed, 19 insertions(+), 4 deletions(-)
---
diff --git a/README.md b/README.md
index 8ba5cf5..b2d97e5 100644
--- a/README.md
+++ b/README.md
@@ -18,17 +18,32 @@ It is desirable to have a wide mix of themes and colors for the additional wallp
 
 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
+#### Technical 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.
+##### Resolution
 
-#### Sharpness
+It is recommended to submit wallpapers of 4megapixels and above. This isn't a hard requirement for sharp 
noiseless cases (see below), but a good rule of thumb.
+
+##### Aspect Ratio
+
+Specific aspect ratio isn't mandated, all wallpapers are scaled 'to cover' in CSS terms (cropped to fit 
display). Do take various possible display aspect ratios into consideration when submitting wallpapers with 
strong reliance on composition.
+
+##### File size
+
+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.
+
+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. 
+
+##### 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 on super wide 
screens where it's cropped to fit and is presented at 1:1 or even scaled up in some cases. Many otherwise 
suitable background images just fall short when observed at the nominal pixel view. Chromatic aberation and 
noise is also something that becomes apparent as you approach 1:1.
 
 ![Bad Scaling](badscaling.jpg)
 
+##### Color Banding
+
+Images should look decent even on lower quality displays. Techniques such as dithering should be used for 
elements with low contrast areas that would otherwise be prone for color banding.
 
 ## License
 
-CCBYSA / Public Domain / CC0 is preferred. All attribution goes to the AUTHORS file.
+CCBYSA / Public Domain / CC0 is preferred. Authorship does need to be sourced, all attribution goes to the 
AUTHORS file.
diff --git a/backgrounds/Stripes.jpg b/backgrounds/Stripes.jpg
index d82ba3e..3e1201c 100644
Binary files a/backgrounds/Stripes.jpg and b/backgrounds/Stripes.jpg differ
diff --git a/backgrounds/Symbolics-1.png b/backgrounds/Symbolics-1.png
index bf3b289..511d690 100644
Binary files a/backgrounds/Symbolics-1.png and b/backgrounds/Symbolics-1.png differ