dev-community.txt: Move 'System Design' into 'Project Information' section
dev-community.txt: Move 'System Design' into 'Project Information' section

The system design doc discusses high-level considerations about the
project, which makes the 'Project Infomation' section a more suitable
place to contain this link.

Change-Id: Iee4a1bef6bf800ff3d96b063fdb22f1502005d98
Signed-off-by: Edwin Kempin <d43fb6c98c97e553b671ed9a9318100f1de386e7@google.com>

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