add a README to the ocis package

ocis/README.md

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+# ocis
+
+The ocis package contains the Infinite Scale runtime and the commands for the Infinite Scale cli.
+
+## Service registry
+
+This package also configures the service registry which will be used to lookup the service addresses. It defaults to mDNS, so mind that, when using systems with mDNS disabled by default (i.e SUSE).
+
+Available registries are:
+
+-   nats
+-   kubernetes
+-   etcd
+-   consul
+-   memory
+-   mdns (default)
+
+To configure which registry to use you have to set the environment variable `MICRO_REGISTRY` and for all except `memory` and `mdns` you also have to set the registry address via `MICRO_REGISTRY_ADDRESS`.
+
+### etcd
+
+To authenticate the connection to the etcd registry you have to set `ETCD_USERNAME` and `ETCD_PASSWORD`.