apk: explicitly enable help

Explicitly enable help so that the build will fail when an appropriate
lua binary isn't found instead of silently disabling the feature.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>

package/system/apk/Makefile

@@ -55,6 +55,7 @@ MESON_VARS+=VERSION=$(PKG_VERSION)
 MESON_COMMON_ARGS = \
 	-Dcompressed-help=false \
 	-Ddocs=disabled \
+	-Dhelp=enabled \
 	-Dlua_version=5.1 \
 	-Durl_backend=wget \
 	-Dzstd=false