add arm64 instructions

README.md

@@ -5,3 +5,16 @@ There are two environments that can be started from this repo: One for the stepu
 You can find more information in their respective directories (stepup and core)
 
 Feedback welcome!
+
+## Mac M1/M2/M3 support
+This branch `feature/arm` adds support for running OpenConext on Macbooks M1/M2/M3 with arm64 processors.
+It _almost_ works out of the box.  The following underlying issues should be solved to make this work without changes:
+ - our upstream java images (`https://hub.docker.com/_/eclipse-temurin`) don't support arm64 in the alpine flavours; we
+   should consider switching to the Ubuntu flavours.  We work around this by running amd64 containers for the java apps
+   (using Rosetta).
+ - our upstream bitnami mongo images don't support arm64.  The issue is that upstream ongo only officially supports
+   arm64 on Ubuntu, whereas bitname build on top of Debian images.  Solved here by using a forked bitnami repo.  We
+   could consider switching to the official Mongo images.
+
+
+To get this to work, you need a an arm64 VM which supports Rosetta. Docker Desktop supports this, or use Parallels.