README.md: use white CNCF logo for a dark GitHub theme

Signed-off-by: Oleksandr Redko <[email protected]>

Author: alexandear

README.md

@@ -75,6 +75,9 @@ Lima follows the [CNCF Code of Conduct](https://github.com/cncf/foundation/blob/
 - - -
 **We are a [Cloud Native Computing Foundation](https://cncf.io/) sandbox project.**
 
-<img src="https://www.cncf.io/wp-content/uploads/2022/07/cncf-color-bg.svg" width=300 />
+<picture>
+  <source media="(prefers-color-scheme: dark)" srcset="https://www.cncf.io/wp-content/uploads/2022/07/cncf-white-logo.svg">
+  <img src="https://www.cncf.io/wp-content/uploads/2022/07/cncf-color-bg.svg" width=300 />
+</picture>
 
 The Linux Foundation® (TLF) has registered trademarks and uses trademarks. For a list of TLF trademarks, see [Trademark Usage](https://www.linuxfoundation.org/trademark-usage/).