Better document genericisation of virtual CPU classes

fixes f3ea6fe02 (#1189), 84f4d6ae2, and 666cb3939

src/BizHawk.Emulation.Cores/CPUs/FairchildF8/F3850.cs

@@ -29,6 +29,11 @@ namespace BizHawk.Emulation.Cores.Components.FairchildF8
 	///
 	/// Note: Programmable timer and interrupt logic from the F3851 is not currently emulated
 	/// </summary>
+	/// <remarks>
+	/// this type parameter might look useless—and it is—but after monomorphisation,
+	/// this way happens to perform better than the alternative
+	/// </remarks>
+	/// <seealso cref="IF3850Link"/>
 	public sealed partial class F3850<TLink> where TLink : IF3850Link
 	{
 		// operations that can take place in an instruction

src/BizHawk.Emulation.Cores/CPUs/MOS 6502X/MOS6502X.cs

@@ -5,6 +5,11 @@ using BizHawk.Emulation.Common;
 
 namespace BizHawk.Emulation.Cores.Components.M6502
 {
+	/// <remarks>
+	/// this type parameter might look useless—and it is—but after monomorphisation,
+	/// this way happens to perform better than the alternative
+	/// </remarks>
+	/// <seealso cref="IMOS6502XLink"/>
 	public sealed partial class MOS6502X<TLink> where TLink : IMOS6502XLink
 	{
 		private readonly TLink _link;

src/BizHawk.Emulation.Cores/CPUs/Z80A/Z80A.cs

@@ -7,6 +7,11 @@ using BizHawk.Common.NumberExtensions;
 // Z80A CPU
 namespace BizHawk.Emulation.Cores.Components.Z80A
 {
+	/// <remarks>
+	/// this type parameter might look useless—and it is—but after monomorphisation,
+	/// this way happens to perform better than the alternative
+	/// </remarks>
+	/// <seealso cref="IZ80ALink"/>
 	public sealed partial class Z80A<TLink> where TLink : IZ80ALink
 	{
 		// operations that can take place in an instruction