add kernel build infra and introduce development guide to README

kernel/.gitignore

@@ -0,0 +1,2 @@
+linux-*
+target/

kernel/build.sh

@@ -0,0 +1,22 @@
+#!/bin/sh
+set -e
+
+cd "$(dirname "${0}")"
+
+# shellcheck source=config.sh
+. "${PWD}/config.sh"
+
+if [ ! -f "${SRC_DIR_NAME}/Makefile" ]
+then
+  rm -rf "${SRC_DIR_NAME}"
+  curl -L -o "${SRC_DIR_NAME}.txz" "${KERNEL_SRC_URL}"
+  tar xvf "${SRC_DIR_NAME}.txz"
+  rm "${SRC_DIR_NAME}.txz"
+fi
+
+mkdir -p "${OUTPUT_DIR_NAME}"
+
+cp hypha.config "${SRC_DIR_NAME}/.config"
+make -C "${SRC_DIR_NAME}" "${@}" olddefconfig
+make -C "${SRC_DIR_NAME}" "${@}" bzImage
+cp "${SRC_DIR_NAME}/arch/x86/boot/bzImage" "${OUTPUT_DIR_NAME}/kernel"

kernel/config.sh

@@ -0,0 +1,5 @@
+#!/bin/sh
+KERNEL_VERSION="6.7.5"
+KERNEL_SRC_URL="https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-${KERNEL_VERSION}.tar.xz"
+SRC_DIR_NAME="linux-${KERNEL_VERSION}"
+OUTPUT_DIR_NAME="out"