[U-Boot] [PATCH v2 16/28] README: Add instructions for chain-loading U-Boot

[sjg at google.com]

Most Chromebooks support chain-loading U-Boot but instructions are
somewhat scattered. Add a README to hold this information within the
U-Boot tree. Also add the standard developer keys to simplify the
instructions, since they are small.

For now this only supports nyan-big.

Signed-off-by: Simon Glass <sjg at chromium.org>
---

Changes in v2:
- Explain how to create dummy.txt
- Add a comment about how to create a protective MBR

 doc/README.chromium                          | 182 +++++++++++++++++++++++++++
 doc/chromium/devkeys/kernel.keyblock         | Bin 0 -> 1208 bytes
 doc/chromium/devkeys/kernel_data_key.vbprivk | Bin 0 -> 1199 bytes
 3 files changed, 182 insertions(+)
 create mode 100644 doc/README.chromium
 create mode 100644 doc/chromium/devkeys/kernel.keyblock
 create mode 100644 doc/chromium/devkeys/kernel_data_key.vbprivk

Applied to u-boot-dm, thanks!