docs/rust: add note about git dependencies

doc/languages-frameworks/rust.section.md

@@ -50,6 +50,11 @@ 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:
 
+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`
+section.
+
 ```nix
   cargoHash = "sha256-l1vL2ZdtDRxSGvP0X/l3nMw8+6WF67KPutJEzUROjg8=";
 ```