fix: update outdated links to external resources

book/src/contributing.md

@@ -49,7 +49,7 @@ into the canonical spec.
 ## Rust
 
 Lighthouse adheres to Rust code conventions as outlined in the [**Rust
-Styleguide**](https://github.com/rust-dev-tools/fmt-rfcs/blob/master/guide/guide.md).
+Styleguide**](https://github.com/rust-lang/rust/tree/HEAD/src/doc/style-guide/src).
 
 Please use [clippy](https://github.com/rust-lang/rust-clippy) and
 [rustfmt](https://github.com/rust-lang/rustfmt) to detect common mistakes and

book/src/homebrew.md

@@ -31,6 +31,6 @@ Alternatively, you can find the `lighthouse` binary at:
 
 The [formula][] is kept up-to-date by the Homebrew community and a bot that lists for new releases.
 
-The package source can be found in the [homebrew-core](https://github.com/Homebrew/homebrew-core/blob/master/Formula/lighthouse.rb) repo.
+The package source can be found in the [homebrew-core](https://github.com/Homebrew/homebrew-core/blob/master/Formula/l/lighthouse.rb) repo.
 
   [formula]: https://formulae.brew.sh/formula/lighthouse

book/src/merge-migration.md

@@ -207,6 +207,6 @@ guidance for specific setups.
 
 - [Ethereum.org: The Merge](https://ethereum.org/en/upgrades/merge/)
 - [Ethereum Staking Launchpad: Merge Readiness](https://launchpad.ethereum.org/en/merge-readiness).
-- [CoinCashew: Ethereum Merge Upgrade Checklist](https://www.coincashew.com/coins/overview-eth/ethereum-merge-upgrade-checklist-for-home-stakers-and-validators)
+- [CoinCashew: Ethereum Merge Upgrade Checklist](https://www.coincashew.com/coins/overview-eth/archived-guides/ethereum-merge-upgrade-checklist-for-home-stakers-and-validators)
 - [EthDocker: Merge Preparation](https://eth-docker.net/About/MergePrep/)
 - [Remy Roy: How to join the Goerli/Prater merge testnet](https://github.com/remyroy/ethstaker/blob/main/merge-goerli-prater.md)