README.md: Update reference to linux SubmittingPatches
The wise linux gods went an moved the content. May as well point to the
actual content.
@@ -100,7 +100,8 @@ git commit -s
git format-patch
```
-You probably want to read the linux Documentation/SubmittingPatches as
+You probably want to read the linux
+https://kernel.org/doc/html/latest/process/submitting-patches.html as
much of it applies to skiboot.
## License
