runtime(doc): include vietnamese.txt

Since Vietnamese keymaps in Vim is quite differences from the
corresponding input methods, let's document the Vietnamese specifics in
vietnames.txt

related: #16144

Signed-off-by: Phạm Bình An <111893501+brianhuster@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/Make_all.mak b/runtime/doc/Make_all.mak
index ccc429b..1715382 100644
--- a/runtime/doc/Make_all.mak
+++ b/runtime/doc/Make_all.mak
@@ -152,6 +152,7 @@
 	vim9.txt \
 	vim9class.txt \
 	visual.txt \
+	vietnamese.txt \
 	windows.txt \
 	workshop.txt
 
@@ -303,6 +304,7 @@
 	version8.html \
 	version9.html \
 	vi_diff.html \
+	vietnamese.html \
 	vimindex.html \
 	vim9.html \
 	vim9class.html \