Update notes for submitted changes

* initramfs: remove "compression mode" choice
* getenv() may return NULL if given environment variable does not exist which leads to NULL dereference when calling strncat.
* gen_init_cpio: remove redundant empty line
* gen_init_cpio: avoid stack overflow when expanding
* kconfig: update compression algorithm info
* arm: add support for LZ4-compressed kernel
* scripts/gen_initramfs_list.sh: fix flags for initramfs LZ4 compression
* initramfs: read CONFIG_RD_ variables for initramfs compression
* lib: add weak clz/ctz functions
* lz4: add overrun checks to lz4_uncompress_unknownoutputsize()
* lz4: fix another possible overrun
* lz4: ensure length does not wrap
* lz4: fix compression/decompression signedness mismatch
* lib/lz4: correct the LZ4 license
* lib: add lz4 compressor module
* lib: add support for LZ4-compressed kernel
* decompressor: add LZ4 decompressor module