README: add maintenance notice

Closes varietywalls#736

Author: jlu5

README.md

@@ -1,10 +1,12 @@
+**Variety is in [maintenance mode](https://github.com/varietywalls/variety/issues/736). While we appreciate your interest, the current maintainers do not have the time to triage all issues and make major changes to the project.**
+
 # Variety
 
-Variety is a wallpaper manager for Linux systems. It supports out-of-the-box most Linux desktop environments, and can be configured to work 
+Variety is a wallpaper manager for Linux systems. It supports out-of-the-box most Linux desktop environments, and can be configured to work
 on more esoteric ones.
 
-It can use local images or automatically download wallpapers from Flickr, Wallhaven, Unsplash, Bing, Reddit and other online sources, 
-allows you to rotate them on a regular interval, and provides easy ways to separate the great images from the junk. 
+It can use local images or automatically download wallpapers from Flickr, Wallhaven, Unsplash, Bing, Reddit and other online sources,
+allows you to rotate them on a regular interval, and provides easy ways to separate the great images from the junk.
 Variety can also display wise and funny quotations or a nice digital clock on the desktop.
 
 Where supported, Variety sits as a tray icon to allow easy pausing and resuming.