[PATCH] binman: Document the __bss_size symbol error

[Simon Glass]

Add a note about the message so it is clear why it occurs.

Signed-off-by: Simon Glass <sjg at chromium.org>
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 tools/binman/binman.rst | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

Applied to u-boot-dm, thanks!