FAQ "How can I add a new configuration?" does not contain answer

[pelepelin]

https://github.com/sbt/website/blob/1.x/src/reference/05-Faq/00.md#how-can-i-add-a-new-configuration is named "How can I add a new configuration?", but the actual example is removed in 685e7d8#diff-388cf1faa6d9a04775ceaf8925a5947fL448 without a new-style replacement.

There is some information about adding new configurations spread in
http://www.scala-sbt.org/1.x/docs/Testing.html#additional-test-configurations
http://www.scala-sbt.org/1.x/docs/Library-Management.html#ivy-configurations
http://www.scala-sbt.org/1.x/docs/Advanced-Configurations-Example.html