Fix and enrich README.md

[yihuajack]

Previous example 1 seems problematic:

Traceback (most recent call last): File "/home/ayka-tsuzuki/.local/bin/sootty", line 8, in sys.exit(main()) File "/home/ayka-tsuzuki/.local/lib/python3.9/site-packages/sootty/main.py", line 94, in main raise Exception( Exception: Unknown wires {'core.inst', 'core.pc'} The following wires were detected in the wiretrace: {'inst', 'mem_write', 'write_next', 'pc_next', 'in1', 'sreg', 'reg_dst', 'alu_op', 'addr', 'waddr_next', 'opcode', 'clk', 'sdata', 'in2', 'pc', 'op', 'alu_in1', 'alu_out', 'wreg', 'mem_read', 'branch', 'wdata_next', 'alu_src', 'funct', 'treg', 'reg_write', 'mem_to_reg', 'alu_shift', 'out', 'zero', 'rst_n', 'i', 'wdata', 'immed', 'wreg_next', 'tdata', 'rdata', 'alu_in2'}

Wires are supposed to be pc and inst, otherwise not runnable.