Add docs

Author: nicolasstucki

compiler/src/dotty/tools/dotc/core/tasty/DottyUnpickler.scala

@@ -37,6 +37,7 @@ object DottyUnpickler {
 
 /** A class for unpickling Tasty trees and symbols.
  *  @param bytes         the bytearray containing the Tasty file from which we unpickle
+ *  @param mode          the tasty file contains package (TopLevel), an expression (Term) or a type (TypeTree)
  */
 class DottyUnpickler(bytes: Array[Byte], mode: UnpickleMode = UnpickleMode.TopLevel) extends ClassfileParser.Embedded with tpd.TreeProvider {
   import tpd._