Add example resource usage on Artix 7

[mithro]

It would be really good to include some information in the README around the resource usage of microwatt.

I would recommend the following stats;

• [ ] LUT + FF usage
• [ ] Highest fmax possible
• [ ] DMIPS/Mhz
• [ ] Coremark/Mhz

It would also be good to include the information for multiple FPGAs like;

• [ ] Xilinx Artix 7 using Vivado
• [ ] Lattice ECP5 using Diamond

It would make it easy to quickly compare it against various other soft processors like Microblaze from Xilinx.

It might also be worth looking at Everyone’s a Critic: A Tool for Exploring RISC-V Projects Paper from FPL to see some ways to benchmark. There is also the awesome An inventory of soft processor cores but it is a little out of date.

[carlosedp]

How big would be the effort to run microwatt on a different fpga? I have a Microsemi Polarfire and would love to try this on it. Thanks.