docs: credit Konrad EISELE for the initial multilib support

Konrad submitted an initial patch adding multlib support:
http://sourceware.org/ml/crossgcc/2011-11/msg00040.html

The patch was full of good ideas, but had a few issues, so
I (Yann E. MORIN) started it all from scatch, re-using part
of the original patch. This got implemented in this series:
hg log -r 446a17b5dd1e:e47d17391ae3

As I forgot to credit Konrad in these changelogs, update the
docs so that the work by Konrad gets credited. Without his
initial effort, we would probably not have had multlib support
so soon. Thank you Konrad!

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

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