Apply suggestions from code review

Author: Byron

gitoxide-core/src/repository/diff.rs

@@ -169,7 +169,6 @@ pub fn file(
     let algorithm = match outcome.operation {
         Operation::InternalDiff { algorithm } => algorithm,
         Operation::ExternalCommand { .. } => {
-            // `unreachable!` is also used in [`Platform::lines()`](gix::object::blob::diff::Platform::lines()).
             unreachable!("We disabled that")
         }
         Operation::SourceOrDestinationIsBinary => {

src/plumbing/options/mod.rs

@@ -519,10 +519,10 @@ pub mod diff {
         },
         /// Diff two versions of a file.
         File {
-            /// A rev-spec representing the 'before' or old tree.
+            /// A rev-spec representing the 'before' or old state of the file, like '@~100:file'
             #[clap(value_parser = crate::shared::AsBString)]
             old_revspec: BString,
-            /// A rev-spec representing the 'after' or new tree.
+            /// A rev-spec representing the 'after' or new state of the file, like ':file'
             #[clap(value_parser = crate::shared::AsBString)]
             new_revspec: BString,
         },