[pkg] add package_in_docker targets

Makefile

@@ -206,8 +206,17 @@ prepare_done:
 # packaging action
 #########################################################################
 
+builder_image:
+	@make -C docker build
+
 packages: package_deb package_snap package_osx package_win
 
+package_snap_in_docker:
+	@make -C docker package_snap
+
+package_win_in_docker:
+	@make -C docker package_win
+
 package_snap:
 	@make -C build/${PROVIDER} pkg_snap
 

docker/README.md

 You can use the makefile to build the image.
+
 "make packages" will build packages inside the builder container.
 
 Use https://github.com/kalikaneko/squid-in-a-can if you want to save some bandwith while building your images.

docker/builder.sh

@@ -12,7 +12,7 @@ case $TYPE in
         echo "[+] Building SNAP"
         make package_snap
         ;;
-    default)
+    *)
         make build
         ;;
 esac