Added information about cluster configuration. This Fixes #106 (#108)

Added information about cluster configuration. Closes #106

Author: ufobat

README.md

@@ -43,9 +43,12 @@ In addition, a few environment variables are provided to set very common paramet
 * `COUCHDB_USER` and `COUCHDB_PASSWORD` will create an ini-file based local admin user with the given username and password in the file `/opt/couchdb/etc/local.d/docker.ini`.
 * `COUCHDB_SECRET` will set the CouchDB shared cluster secret value, in the file `/opt/couchdb/etc/local.d/docker.ini`.
 * `NODENAME` will set the name of the CouchDB node inside the container to `couchdb@${NODENAME}`, in the file `/opt/couchdb/etc/vm.args`. This is used for clustering purposes and can be ignored for single-node setups.
+* Erlang Environment Variables like `ELR_FLAGS` will be used by Erlang itself. For a complete list have a look [here](http://erlang.org/doc/man/erl.html#environment-variables)
 
 If other configuration settings are desired, externally mount `/opt/couchdb/etc` and provide `.ini` configuration files under the `/opt/couchdb/etc/local.d` directory.
 
+For a CouchDB cluster you need to provide the `NODENAME` setting as well as the erlang cookie. Settings to Erlang can be made with the environment variable `ERL_FLAGS`, e.g. `ERL_FLAGS=-setcookie "brumbrum"`. Further information can be found [here](http://docs.couchdb.org/en/stable/cluster/setup.html).
+
 ### Important notes
 
 Please note that CouchDB no longer autocreates system databases for you. This is intentional; multi-node CouchDB deployments must be joined into a cluster before creating these databases.