docs: erc165 + structs (#304)

Follows up #62

#### PR Checklist

- [ ] Tests
- [x] Documentation

---------

Co-authored-by: Gustavo Gonzalez <gustavo.gonzalez@openzeppelin.com>
(cherry picked from commit c40dc8e)

docs/modules/ROOT/nav.adoc

@@ -9,3 +9,4 @@
 
 * xref:access-control.adoc[Access Control]
 * xref:crypto.adoc[Cryptography]
+* xref:utilities.adoc[Utilities]

docs/modules/ROOT/pages/utilities.adoc

@@ -0,0 +1,43 @@
+= Utilities
+
+The OpenZeppelin Stylus Contracts provides a ton of useful utilities that you can use in your project.
+For a complete list, check out the https://docs.rs/openzeppelin-stylus/0.1.0-rc/openzeppelin_stylus/utils/index.html[API Reference].
+Here are some of the more popular ones.
+
+[[introspection]]
+== Introspection
+
+It's frequently helpful to know whether a contract supports an interface you'd like to use.
+https://eips.ethereum.org/EIPS/eip-165[`ERC-165`] is a standard that helps do runtime interface detection.
+Contracts for Stylus provides helpers for implementing ERC-165 in your contracts:
+
+* https://docs.rs/openzeppelin-stylus/0.1.0-rc/openzeppelin_stylus/utils/introspection/erc165/trait.IErc165.html[`IERC165`] — this is the ERC-165 trait that defines https://docs.rs/openzeppelin-stylus/0.1.0-rc/openzeppelin_stylus/utils/introspection/erc165/trait.IErc165.html#tymethod.supports_interface[`supportsInterface`]. In order to implement ERC-165 interface detection, you should manually expose https://docs.rs/openzeppelin-stylus/0.1.0-rc/openzeppelin_stylus/utils/introspection/erc165/trait.IErc165.html#tymethod.supports_interface[`supportsInterface`] function in your contract.
+
+[source,rust]
+----
+sol_storage! {
+ #[entrypoint]
+ struct Erc721Example {
+ #[borrow]
+ Erc721 erc721;
+ }
+}
+
+#[public]
+#[inherit(Erc721)]
+impl Erc721Example {
+ pub fn supports_interface(interface_id: FixedBytes<4>) -> bool {
+ Erc721::supports_interface(interface_id)
+ }
+}
+
+----
+
+[[structures]]
+== Structures
+
+Some use cases require more powerful data structures than arrays and mappings offered natively in alloy and the Stylus sdk.
+Contracts for Stylus provides these libraries for enhanced data structure management:
+
+- https://docs.rs/openzeppelin-stylus/0.1.0-rc/openzeppelin_stylus/utils/structs/bitmap/index.html[`BitMaps`]: Store packed booleans in storage.
+- https://docs.rs/openzeppelin-stylus/0.1.0-rc/openzeppelin_stylus/utils/structs/checkpoints/index.html[`Checkpoints`]: Checkpoint values with built-in lookups.