Update tag

As part of improving kernel integration with the Hub: https://github.com/huggingface/huggingface.js/pull/1822 , we are using the `kernels` tag in place of `kernel` from now on. This is a small PR to update the tag.

README.md

@@ -1,7 +1,7 @@
 ---
 license: apache-2.0
 tags:
-  - kernel
+  - kernels
   - sae
 ---
 # Flex SAE Kernels