Document Ctrl+J as alternative to Shift+Enter for inserting newlines

Summary

Ctrl+J inserts a newline in the input prompt, behaving identically to Shift+Enter. This is useful for users whose terminal emulators don't support or can't be configured to send Shift+Enter (common with certain terminals, multiplexers, or SSH sessions).

Request

Document Ctrl+J as an alternative keybinding for inserting newlines alongside the existing Shift+Enter documentation. This could be mentioned in:

• The keybindings help/reference
• The README or docs where Shift+Enter is mentioned

Why it matters

• Shift+Enter doesn't work in all terminal setups
• Ctrl+J is a reliable terminal-level alternative (sends ASCII LF)
• Users currently have to discover this on their own