docs(input): document navigate_search arguments

src/input/Binding.zig

@@ -423,6 +423,8 @@ pub const Action = union(enum) {
 
     /// Navigate the search results. If there is no active search, this
     /// is not performed.
+    ///
+    /// Valid arguments: `previous`, `next`.
     navigate_search: NavigateSearch,
 
     /// Start a search if it isn't started already. This doesn't set any