Give credit to Joona for optimized parameters

This also allow us to better track what is already
optimized and what still needs optimization.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/material.cpp

@@ -37,6 +37,7 @@ using std::string;
 
 namespace {
 
+  // Values modified by Joona Kiiski
   const Value BishopPairMidgameBonus = Value(109);
   const Value BishopPairEndgameBonus = Value(97);