doc: update buildRustPackage documentation

Fixes some mistakes regarding the references to cargoHash in the codes referenced.
Fixes a typo for cargoSha256.
States that cargoHash should be preferred.

doc/languages-frameworks/rust.section.md

@@ -44,20 +44,21 @@ rustPlatform.buildRustPackage rec {
 }
 ```
 
-`buildRustPackage` requires either the `cargoSha256` or the
-`cargoHash` attribute which is computed over all crate sources of this
-package. `cargoHash256` is used for traditional Nix SHA-256 hashes,
-such as the one in the example above. `cargoHash` should instead be
-used for [SRI](https://www.w3.org/TR/SRI/) hashes. For example:
+`buildRustPackage` requires either the `cargoHash` or the `cargoSha256`
+attribute which is computed over all crate sources of this package.
+`cargoSha256` is used for traditional Nix SHA-256 hashes. `cargoHash` should
+instead be used for [SRI](https://www.w3.org/TR/SRI/) hashes and should be
+preferred. For example:
+
+```nix
+  cargoHash = "sha256-l1vL2ZdtDRxSGvP0X/l3nMw8+6WF67KPutJEzUROjg8=";
+```
 
 Exception: If the application has cargo `git` dependencies, the `cargoHash`/`cargoSha256`
 approach will not work, and you will need to copy the `Cargo.lock` file of the application
-to nixpkgs and continue with the next section for specifying the options of the`cargoLock`
+to nixpkgs and continue with the next section for specifying the options of the `cargoLock`
 section.
 
-```nix
-  cargoHash = "sha256-l1vL2ZdtDRxSGvP0X/l3nMw8+6WF67KPutJEzUROjg8=";
-```
 
 Both types of hashes are permitted when contributing to nixpkgs. The
 Cargo hash is obtained by inserting a fake checksum into the