Mention possible run options in the task modal placeholder (#8449)

Release Notes:

- Improved run task modal's placeholder

---------

Co-authored-by: Piotr Osiewicz <24362066+osiewicz@users.noreply.github.com>

crates/tasks_ui/src/modal.rs

@@ -23,7 +23,6 @@ pub(crate) struct TasksModalDelegate {
     candidates: Vec<Arc<dyn Task>>,
     matches: Vec<StringMatch>,
     selected_index: usize,
-    placeholder_text: Arc<str>,
     workspace: WeakView<Workspace>,
     last_prompt: String,
 }
@@ -36,7 +35,6 @@ impl TasksModalDelegate {
             candidates: Vec::new(),
             matches: Vec::new(),
             selected_index: 0,
-            placeholder_text: Arc::from("Select task..."),
             last_prompt: String::default(),
         }
     }
@@ -115,8 +113,12 @@ impl PickerDelegate for TasksModalDelegate {
         self.selected_index = ix;
     }
 
-    fn placeholder_text(&self, _cx: &mut WindowContext) -> Arc<str> {
-        self.placeholder_text.clone()
+    fn placeholder_text(&self, cx: &mut WindowContext) -> Arc<str> {
+        Arc::from(format!(
+            "{} runs the selected task, {} spawns a bash-like task from the prompt",
+            cx.keystroke_text_for(&menu::Confirm),
+            cx.keystroke_text_for(&menu::SecondaryConfirm),
+        ))
     }
 
     fn update_matches(