kernel: Fix up README.md
The content about debug was no longer valid.
-See [../docs/kernels.md](../docs/kernels.md) for more
-information on kernel builds.
-
-To build with various debug options enabled, build the kernel with
-`make DEBUG=1`. The options enabled are listed in `kernel_config.debug`.
-This allocates a significant amount of memory on boot and you may need to
-adjust the kernel config on some systems. Specifically:
-
-```diff
---- a/alpine/kernel/kernel_config
-+++ b/alpine/kernel/kernel_config
-@@ -415,8 +415,8 @@ CONFIG_DMI=y
- # CONFIG_CALGARY_IOMMU is not set
- CONFIG_SWIOTLB=y
- CONFIG_IOMMU_HELPER=y
--CONFIG_MAXSMP=y
--CONFIG_NR_CPUS=8192
-+CONFIG_MAXSMP=n
-+CONFIG_NR_CPUS=8
- # CONFIG_SCHED_SMT is not set
- CONFIG_SCHED_MC=y
- # CONFIG_PREEMPT_NONE is not set
-```
+See [../docs/kernels.md](../docs/kernels.md) for more information on kernel builds.
