[indic-like] Add note about replicated values

src/hb-ot-shaper-indic-machine.rl

@@ -55,6 +55,7 @@ enum indic_syllable_type_t {
 
 %%{
 
+# These values are replicated from indic.hh; keep in sync.
 export C    = 1;
 export V    = 2;
 export N    = 3;

src/hb-ot-shaper-khmer-machine.rl

@@ -54,6 +54,7 @@ enum khmer_syllable_type_t {
 
 %%{
 
+# These values are replicated from indic.hh; keep in sync.
 export C    = 1;
 export V    = 2;
 export ZWNJ = 5;

src/hb-ot-shaper-myanmar-machine.rl

@@ -57,6 +57,7 @@ enum myanmar_syllable_type_t {
 
 %%{
 
+# These values are replicated from indic.hh; keep in sync.
 export C    = 1;
 export IV   = 2;
 export DB   = 3;	# Dot below	     = OT_N