Installation docs for Raspberry-Pi missing supported architecture requirement #5772

Old document "demos/Raspberry-Pi/README.md" had this info:

Note that CoreCLR (and thus PowerShell Core) will only work on Pi 2 and Pi 3 devices as other devices like Pi Zero have an unsupported processor.

but new document "docs/installation/linux.md" is missing this info and that confuses some users who try to run PS on RPI-1/0.
"docs/installation/linux.md" should be updated.