Rewrite of 'Adjust correction history' condition

Current condition is convoluted and hard to understand because of
several negations. Also added 2 comments to make the concept behind the
condition better understandable.

No functional change

src/search.cpp

@@ -1332,9 +1332,9 @@ Value Search::Worker::search(
                        depth, bestMove, unadjustedStaticEval, tt.generation());
 
     // Adjust correction history
-    if (!ss->inCheck && (!bestMove || !pos.capture(bestMove))
-        && !(bestValue >= beta && bestValue <= ss->staticEval)
-        && !(!bestMove && bestValue >= ss->staticEval))
+    if (!ss->inCheck && !(bestMove && pos.capture(bestMove))
+        && ((bestValue < ss->staticEval && bestValue < beta)  // negative correction & no fail high
+            || (bestValue > ss->staticEval && bestMove)))     // positive correction & no fail low
     {
         const auto m = (ss - 1)->currentMove;