pinmap: Correct some link errors in README.md
pinmap: Correct some link errors in README.md

Some documentation correction.

BUG=none
TEST=none
BRANCH=none

Signed-off-by: Andrew McRae <44ad1424cfc8411c96d9181798ca41ae55709dfb@google.com>
Change-Id: I587f028d7c88d9fa6349a09646611006267a4b1a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3354266
Reviewed-by: Peter Marheine <ef0b2c492edde94778d7465bfbaeed52c5be6858@chromium.org>
Commit-Queue: Peter Marheine <ef0b2c492edde94778d7465bfbaeed52c5be6858@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec