doc: fix comment

Author: boriel

src/zxbc/zxbc.py

@@ -153,7 +153,7 @@ def main(args=None, emitter=None):
 
     # Join all lines into a single string and ensures an INTRO at end of file
     asm_output = backend.emit(backend.MEMORY, optimize=OPTIONS.optimization_level > 0)
-    asm_output = arch.target.optimizer.optimize(asm_output) + "\n"  # invoke the -O3
+    asm_output = arch.target.optimizer.optimize(asm_output) + "\n"  # invoke the peephole optimizer
 
     asm_output = asm_output.split("\n")
     for i in range(len(asm_output)):