Installation on PC does not detect correct platform

[Peter-van-Tol]

Describe the bug
On a 64-bit PC, it is reported as i386, which is wrong. This leads to OSS-CAD-suite not being installed when using the command install_toolchain.

To Reproduce
On a 64-bit system, execute the command litexcnc install_toolchain

Additional context
Together with this bug, the following things can be improved:

• install OpenOCD on all Linux platforms (currently it is only installed on ARM devices such as RPi);
• install git before installing Litex, to prevent errors when this program is not present;
• improve documentation, by including a tutorial with the steps as described in Welcome to LiteX-CNC Discussions! #35 (comment)

[Peter-van-Tol]

Done so far:

• Resolve the bug regarding the detection of 64-bit platforms;
• Install OpenOCD on Linux platforms;
• Install git before installing Litex.

Next thing to do: documentation

[Peter-van-Tol]

Re-opening the issue for documentation purposes