chore: add dark/light mode banners for the root readme (#7)

Author: maxprilutskiy

content/banner.dark.png

@@ -1 +1,4 @@
-![banner](./content/banner.png)
+<p align="center">
+<img src="./content/banner.light.png#gh-light-mode-only">
+<img src="./content/banner.dark.png#gh-dark-mode-only">
+</p>