Add dockerfile

Dockerfile

@@ -0,0 +1,3 @@
+FROM wiiuenv/devkitppc:20200625
+
+WORKDIR project

README.md

@@ -8,6 +8,21 @@ Place the `payload.elf` in the `sd:/wiiu` folder of your sd card and run a explo
 
 For building you just need [wut](https://github.com/devkitPro/wut/) installed, then use the `make` command.
 
+## Building using the Dockerfile
+
+It's possible to use a docker image for building. This way you don't need anything installed on your host system.
+
+```
+# Build docker image (only needed once)
+docker build . -t customrpxloader-builder
+
+# make 
+docker run -it --rm -v ${PWD}:/project customrpxloader-builder make
+
+# make clean
+docker run -it --rm -v ${PWD}:/project customrpxloader-builder make clean
+```
+
 ## Credits
 - Maschell
 - orboditilt