Update copy (#1935)

Updated copy

---------

Co-authored-by: pap-openai <pap@openai.com>

codex-rs/tui/src/bottom_pane/chat_composer.rs

@@ -31,7 +31,7 @@ use crate::bottom_pane::textarea::TextAreaState;
 use codex_file_search::FileMatch;
 use std::cell::RefCell;
 
-const BASE_PLACEHOLDER_TEXT: &str = "...";
+const BASE_PLACEHOLDER_TEXT: &str = "Ask Codex to do anything";
 /// If the pasted content exceeds this number of characters, replace it with a
 /// placeholder in the UI.
 const LARGE_PASTE_CHAR_THRESHOLD: usize = 1000;