[seL4] suggestion; update faq reference to ODROID-C2

Hello,

The faq section on "How can I build a system with seL4?" [1] has an obsoleted/discountinued product pointing to ODROID-C2 [2] a current product such as the one from OnLogic can replace, perhaps. [3]

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If you have access to an Odroid-C2, you should be able to do the project work yourself as a way of familiarising yourself with seL4.

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[1] https://docs.sel4.systems/projects/sel4/frequently-asked-questions.html

[2] https://www.hardkernel.com/shop/odroid-c2/

[3] https://www.onlogic.com/industrial-raspberry-pi/