The createIndexes command accepts a write concern – we should add this fact (and examples) to https://docs.mongodb.com/manual/reference/command/createIndexes/
Additionally, we should add reference links to https://docs.mongodb.com/manual/reference/command/createIndexes/ and its shell helper page at https://docs.mongodb.com/manual/reference/method/db.collection.createIndex/ so that it is easy to go between the two pages.