OPNSense/tools ea51558. README.md, build arm.sh

device: there is no RPI3 support in 11.2

Add it later when we have it, because if we keep it there will
only be questions why it doesn't work.
DeltaFile
+0-36config/19.1/SMP-RPI3
+0-16build/arm.sh
+0-11device/rpi3.conf
+1-1README.md
+1-644 files

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