Re-added app_sdk to main repo with MIT

backend/app_sdk/README.md

@@ -0,0 +1,16 @@
+# app_sdk.py
+This is the SDK used for apps to behave like they should. 
+To change it in the backend, upload it to Buckets/shuffler.appspot.com/generated_apps/baseline.
+
+# static_baseline.py
+It's used for python code generation and should be under MIT. Has to be located here because it's used by the backend.
+
+## If you want to update apps.. PS: downloads from docker hub do overrides.. :)
+1. Write your code & check if runtime works
+2. Build app_base image
+3. docker rm $(docker ps -aq) # Remove all stopped containers
+4. Delete the specific app's Docker image (docker rmi frikky/shuffle:...)
+5. Rebuild the Docker image (click load in GUI?)
+
+# LICENSE 
+Everything in here is MIT, not AGPLv3 as indicated by the license.