fix(Risc-V toolchain): don't hardcode absolute path in /opt

[mratsim]

The installation path of riscv32-unknown-elf-gcc is distro-specific. For example in mine it's in the standard /usr/bin, instead of non-standard /opt/riscv/bin/

The standard way to make binary available regardless of physical location (local, opt, /usr/bin) is to add them to $PATH, which I assume any installer is doing.

[CeciliaZ030]

you also gotta change here

raiko/script/install.sh

Line 21 in 18bbfc9

mkdir /opt/riscv

if you want to make it distro-specific :)

[mratsim]

For now this PR is paused, I think we need to review the install script maybe we need one for users and one for Github Actions. The current one assumes Docker and root permissions.

See #299