Added TBinomialCoefficientCache method documentation

UBinomialCoefficients.pas

@@ -37,7 +37,10 @@ type
   public
     constructor Create;
     destructor Destroy; override;
+    // Returns N choose K, with N >= K >= 0.
     function Get(const AN, AK: Cardinal): Cardinal;
+    // Returns the number of cached rows C = N + 1, where N is the highest from previously queried "N choose K". The
+    // actual number of cached binomial coefficient values is C * (C + 1) / 2.
     function GetCachedRowsCount: Cardinal;
   end;