[minor] Fix README code example to use new instruction mnemonic
@@ -113,7 +113,7 @@ You can correlate the trace...
f42c: 1d 20 14 82 store_8 s0, 1288(sp)
f430: 60 03 00 ac getcr s27, 0
f434: 5b 03 80 08 setne_i s26, s27, 0
- f438: 1a 02 00 f4 btrue s26, main+772
+ f438: 1a 02 00 f4 bnz s26, main+772
f43c: 1f b0 ef a9 load_32 s0, -1044(pc)
```
