add docs

Author: Skgland

src/prepare.rs

@@ -397,6 +397,7 @@ pub enum PrepareError {
     /// Some of the dependencies do not exist anymore.
     #[error("the crate depends on missing dependencies: \n\n{0}")]
     MissingDependencies(String),
+    /// cargo rejected the lockfile
     #[error("the crate has a broken lockfile: \n\n{0}")]
     InvalidCargoLock(String),
 }