update: using IEquatable with serialization

[NoelStephensUnity]

Adding some additional information about using IEquatable with serialization.

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Purpose of the Pull Request:
To provide additional information about using IEquatable with INetworkSerializable.

Issue Number:
MTTB-1306

[jabbacakes]

Approving with minor wording tweaks

[jabbacakes]

Suggested change

	In order to use an `INetworkSerializable` implementation with `NetworkVariable`, you must also implement the `IEquatable<T>` interface in order to determine whether a value has been updated or not.
	To use an `INetworkSerializable` implementation with `NetworkVariable`, you must also implement the `IEquatable<T>` interface to determine whether a value has been updated or not.

[jabbacakes]

Suggested change

	#### IEquatable and generics
	You might think it would be much simpler to have a single class that could handle all of your serialization in order to avoid replicating some of the base script requirements.
	This is an example of what will not work:
	#### `IEquatable` and generics
	It might seem simpler to have a single class that handles all of your serialization to avoid replicating some of the base script requirements, however there are some issues with this implementation.
	The following is an example of what won't work:

[jabbacakes]

Suggested change

	There are two issues with the above approach:
	- The Netcode for GameObjects ILPP script will be looking for the actual `IEquatable<MyBaseSerializer<int>>` and throw an error.
	- The generic `T` is nullable and cannot be nullable.
	However, there are some things you can do if you would like to use this kind of design pattern. The alternative is to not try and make the base class implement `IEquatable` but to implement it relative to each derived class.
	One example of this would be:
	There are two issues with the approach above:
	- The Netcode for GameObjects ILPP script will be looking for the actual `IEquatable<MyBaseSerializer<int>>` and throw an error.
	- The generic `T` is nullable and cannot be nullable.
	However, there are some things you can do if you want to use this kind of design pattern. The alternative is to not try and make the base class implement `IEquatable` but to implement it relative to each derived class.
	For example:

[jabbacakes]

Suggested change

	Where `MyExtendedData` implements `IEquatable<MyExtendedData>` and overriding the `OnNetworkSerialize` allows one to stack serialization in an ascending or descending order.
	Where `MyExtendedData` implements `IEquatable<MyExtendedData>` and overriding the `OnNetworkSerialize` allows you to stack serialization in an ascending or descending order.

[jabbacakes]

Suggested change

	While the above example is using a class it is recommended to stick with using `struct` when implementing `INetworkSerializable` due to its lower memory footprint and it helps to avoid other serialization related issues when using a class.
	The example above uses a class, but it's generally recommended to use a `struct` when implementing `INetworkSerializable` due to its lower memory footprint. It also helps to avoid other serialization-related issues when using a class.