Update index-modules.asciidoc
Update index-modules.asciidoc

Docs: Clarified `blocks.write` vs `blocks.read_only`
vroyer/elassandra,strapdata/elassandra,strapdata/elassandra,vroyer/elasticassandra,vroyer/elasticassandra,strapdata/elassandra,vroyer/elassandra,strapdata/elassandra,vroyer/elassandra,vroyer/elasticassandra,strapdata/elassandra