add apk-update(8)

doc/Makefile

@@ -8,6 +8,7 @@ docs: $(obj)/apk.8 \
 	$(obj)/apk-add.8 \
 	$(obj)/apk-del.8 \
 	$(obj)/apk-fix.8 \
+	$(obj)/apk-update.8 \
 	$(obj)/apk-repositories.5 \
 	$(obj)/apk-world.5
 targets += docs

doc/apk-update.8.scd

@@ -0,0 +1,24 @@
+apk-update(8)
+
+# NAME
+
+apk update - update repository indexes
+
+# SYNOPSIS
+
+*apk update*
+
+# DESCRIPTION
+
+*apk update* fetches the index from all configured package repositories. See
+*apk-repositories*(5) for more information on configuring package repositories.
+
+# OPTIONS
+
+*apk update* does not support any specific options. See *apk*(8) for global
+options.
+
+# AUTHORS
+
+Natanael Copa <ncopa@alpinelinux.org>++
+Timo Teräs <_timo.teras@iki.fi_>