Merge pull request #363 from Fraser999/update-rustdocs

Mention cyclic dependency in main rustdocs

src/lib.rs

@@ -36,7 +36,11 @@
 //!   (de)serializing [`IndexMap`] as an ordered sequence are available in the
 //!   [`map::serde_seq`] module.
 //! * `borsh`: Adds implementations for [`BorshSerialize`] and [`BorshDeserialize`]
-//!   to [`IndexMap`] and [`IndexSet`].
+//!   to [`IndexMap`] and [`IndexSet`]. **Note:** When this feature is enabled,
+//!   you cannot enable the `derive` feature of [`borsh`] due to a cyclic
+//!   dependency. Instead, add the `borsh-derive` crate as an explicit
+//!   dependency in your Cargo.toml and import as e.g.
+//!   `use borsh_derive::{BorshSerialize, BorshDeserialize};`.
 //! * `arbitrary`: Adds implementations for the [`arbitrary::Arbitrary`] trait
 //!   to [`IndexMap`] and [`IndexSet`].
 //! * `quickcheck`: Adds implementations for the [`quickcheck::Arbitrary`] trait
@@ -50,6 +54,7 @@
 //! [`Deserialize`]: `::serde::Deserialize`
 //! [`BorshSerialize`]: `::borsh::BorshSerialize`
 //! [`BorshDeserialize`]: `::borsh::BorshDeserialize`
+//! [`borsh`]: `::borsh`
 //! [`arbitrary::Arbitrary`]: `::arbitrary::Arbitrary`
 //! [`quickcheck::Arbitrary`]: `::quickcheck::Arbitrary`
 //!