[libadwaita] stylesheet: Make the README Markdown

[Alexander Mikhaylenko <alexm src gnome org>]

commit 54cb1d5208190b5404a96786d257a83d507183ff
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Tue May 25 13:56:47 2021 +0200

    stylesheet: Make the README Markdown
    
    Let's be consistent with our plain text documentation format.

 src/stylesheet/{README => README.md} | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
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diff --git a/src/stylesheet/README b/src/stylesheet/README.md
similarity index 100%
rename from src/stylesheet/README
rename to src/stylesheet/README.md