RUBY-837 Update create_collection and create_index opts documentation

Author: estolfo

lib/mongo/collection.rb

@@ -550,6 +550,8 @@ def update(selector, document, opts={})
     #   The option is silently ignored by the server and unique index builds using the option will
     #   fail if a duplicate value is detected.
     #
+    # @note See the MongoDB documentation for a full list of supported options by server version.
+    #
     # @return [String] the name of the index created.
     def create_index(spec, opts={})
       options              = opts.dup
@@ -581,6 +583,8 @@ def create_index(spec, opts={})
     #   The option is silently ignored by the server and unique index builds using the option will
     #   fail if a duplicate value is detected.
     #
+    # @note See the MongoDB documentation for a full list of supported options by server version.
+    #
     # @return [String] the name of the index.
     def ensure_index(spec, opts={})
       now                  = Time.now.utc.to_i

lib/mongo/db.rb

@@ -316,6 +316,8 @@ def collections_info(coll_name=nil)
     #   either we're in +strict+ mode and the collection
     #   already exists or collection creation fails on the server.
     #
+    # @note See the MongoDB documentation for a full list of supported options by server version.
+    #
     # @return [Mongo::Collection]
     def create_collection(name, opts={})
       name = name.to_s