PicoRV-Softcore documentation

This MR is for GSoC 2024 Project Low-Latency I/O RiscV core on FPGA fabric of BeagleV-Fire.

• I have added prerequisites and detailed steps to use the PicoRV Softcore with BeagleV-Fire.
• The documentation also contains steps to program the Softcore at start and at the run-time.