add notes on architectures

[orangecms]

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We need to add a statement on architecture support.

Just a little "works on all architectures supported by Linux with kexec" will do, with a list of exampleds, "such as RISC-V, Arm, Arm64, and x86".

It might be better to have a "known good" specific list, and add "may work on other architectures supported by Linux".