[TASK] multidomain setup documentation

Author: chrschw

README.md

@@ -674,6 +674,19 @@ in the NodeTypes.yaml. Generally this works by defining the global mapping at `[
         search_analyzer: custom_french_analyzer
 ```
 
+## Change the default Elastic index name
+
+If you need to run serveral (different) neos instances on the same elasticsearch server you will need to change the Configuration/Settings.yaml indexName for each of your project. 
+
+So `./flow nodeindex:build` or `./flow nodeindex:cleanup` won't overwrite your other sites index.
+
+```
+TYPO3:
+  TYPO3CR:
+    Search:
+      elasticSearch:
+        indexName: useMoreSpecificIndexName
+```
 
 ## Debugging