Update create-index.asciidoc
Update create-index.asciidoc

Document defaults for `number_of_shards` and `number_of_replicas`

Closes #5899
vorce/es-metrics,vorce/es-metrics,aparo/elasticsearch,fubuki/elasticsearch,aparo/elasticsearch,fubuki/elasticsearch,fubuki/elasticsearch,fubuki/elasticsearch,fubuki/elasticsearch,aparo/elasticsearch,aparo/elasticsearch,vorce/es-metrics,vorce/es-metrics,fubuki/elasticsearch,vorce/es-metrics,aparo/elasticsearch,aparo/elasticsearch