message: Update selfSustained documentation for clarity
diff: @@ -269,7 +269,7 @@ bool structureIsLander(StructureID id)
  /**
  - * Determines if the structure requires a tube connection or not.
  + * Determines if the structure is able to operate without a tube connection.
  */
  bool selfSustained(StructureID id)
  {
  