improved usability of native docker image

docker/README.md

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+# RBCS Docker images
+There are 3 image flavours:
+- vanilla
+- memcache
+- native
+
+The `vanilla` image only contains the envelope 
+jar file with no plugins and is based on `eclipse-temurin:21-jre-alpine`
+
+The `memcache` image is similar to the `vanilla` image, except that it also contains
+the `rbcs-server-memcache` plugin in the `plugins` folder, use this image if you don't want to use the `native`
+image and want to use memcache as the cache backend
+
+The `native` image contains a native, statically-linked executable created with GraalVM
+that has no userspace dependencies. It also embeds the memcache plugin inside the executable.
+Use this image for maximum efficiency and minimal memory footprint. 
+
+## Which image shoud I use?
+The `native` image uses Java's SerialGC, so it's ideal for constrained environment like containers or small servers,
+if you have a lot of resources and want to squeeze out the maximum throughput you should consider the
+`vanilla` or `memcache` image, then choose and fine tune the garbage collector.
+
+Also the `native` image is only available for the `x86_64` architecture at the moment, 
+while `vanilla` and `memcache` also ship a `aarch64` variant.