Add clarifying comment to empty dependency rule

- Explain that snaccrose.h is generated alongside snaccrose.cpp

Co-authored-by: mouse07410 <5923577+mouse07410@users.noreply.github.com>

Author: Copilot

cxx-lib/automake.mk

@@ -135,6 +135,7 @@ cxx-lib/inc/snacc.h.in: snacc.h.in
 cxx-lib/src/snaccrose.cpp: asn1specs/snaccrose.asn compiler/esnacc$(EXEEXT)
 	$(AM_V_GEN)compiler/esnacc$(EXEEXT) -C -mo cxx-lib/src $<
 
+# Dependency rule - snaccrose.h is generated alongside snaccrose.cpp by the rule above
 cxx-lib/src/snaccrose.h: cxx-lib/src/snaccrose.cpp
 
 cxx-lib/inc/snaccrose.h: cxx-lib/src/snaccrose.h