Add proper descriptions to commands and arguments

Author: cruessler

src/plumbing/options/mod.rs

@@ -388,21 +388,21 @@ pub mod merge {
 pub mod diff {
     use gix::bstr::BString;
 
+    /// Print all changes between two objects
     #[derive(Debug, clap::Parser)]
-    #[command(about = "TODO")]
     pub struct Platform {
         #[clap(subcommand)]
         pub cmd: SubCommands,
     }
 
     #[derive(Debug, clap::Subcommand)]
     pub enum SubCommands {
-        /// TODO
+        /// Diff two trees by specifying their revspecs.
         Tree {
-            /// TODO
+            /// A revspec representing the before or old tree
             #[clap(value_parser = crate::shared::AsBString)]
             old_treeish: BString,
-            /// TODO
+            /// A revspec representing the after or new tree
             #[clap(value_parser = crate::shared::AsBString)]
             new_treeish: BString,
         },