[DOCS] Clarifying docs around multi-resource reads and writes

fixes #990

docs/src/reference/asciidoc/core/configuration.adoc

@@ -26,9 +26,12 @@ es.resource = twitter/tweet   # index 'twitter', type 'tweet'
 `es.resource.write`(defaults to `es.resource`)::
 {es} resource used for writing (but not reading) data. Used typically for __dynamic resource__ writes or when writing and reading data to different {es} indices within the _same_ job. Typically set automatically (except for the {mr} module which requires manual configuration).
 
-Note that https://www.elastic.co/guide/en/elasticsearch/guide/current/multi-index-multi-type.html[multiple] indices and/or types are allowed *only* for reading. Use `_all/types` to search `types` in all indices or `index/` to search
-all types within `index`.
-Do note that reading multiple indices/types typically works only when they have the same structure and only with some libraries. Integrations that require a strongly typed mapping (such as a table like Hive or SparkSQL) are likely to fail.
+Note that specifying https://www.elastic.co/guide/en/elasticsearch/guide/current/multi-index-multi-type.html[multiple]
+indices and/or types in the above resource settings are allowed *only* for reading. Specifying multiple indices for
+writes is only supported through the use of dynamic resource (described <<cfg-multi-writes, below>>). Use `_all/types`
+to search `types` in all indices or `index/` to search all types within `index`. Do note that reading multiple
+indices/types typically works only when they have the same structure and only with some libraries. Integrations that
+require a strongly typed mapping (such as a table like Hive or SparkSQL) are likely to fail.
 
 [[cfg-multi-writes]]
 [float]