[wip] Unity SDK reference

docs/reference/unity.md

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+---
+title: Unity SDK reference
+authors: Tim McMackin
+last_update:
+  date: 6 December 2023
+---
+
+The Tezos SDK for Unity provides several objects that your Unity project can use to work with Tezos.
+These pages provide reference for the most important of these objects:
+
+- [API object](./unity/API): Provides information about the Tezos blockchain, such as what tokens accounts or contracts control
+- [DAppMetadata object](./unity/DAppMetadata): Provides read-only properties that describe the project
+- [MessageReceiver object](./unity/MessageReceiver): Provides events that you can add listeners to, such as when users connect their wallets
+- [TokenContract object](./unity/TokenContract): Provides a built-in FA2-compatible smart contract and convenience methods to work with it
+- [Wallet object](./unity/Wallet): Provides methods to connect to wallets and send transactions from the connected account
+
+The SDK also provides Unity prefabs that are prerequisites for the SDK; see [Prefabs](./unity/prefabs).