readme: document audio recorder requirement (pipewire-bin)

README.md

@@ -72,6 +72,16 @@ menu — just click it. Or run the installed binary directly:
 ```
 
 Requires a glibc-based 64-bit Linux (glibc ≥ 2.38) with a working X11/XCB display.
+
+**Microphone / speech-to-text:** emu records using your system's audio recorder, so
+one of these must be installed (on a standard PipeWire desktop the first is already
+present):
+```bash
+sudo apt install pipewire-bin      # provides pw-record (recommended, PipeWire-native)
+# or: sudo apt install pulseaudio-utils   (parecord)
+# or: sudo apt install alsa-utils         (arecord)
+```
+
 **Getting a model:** open the **model menu** at the top and pick one to download, or
 just **type a prompt and press Enter** — if no model is installed yet, emu downloads
 a recommended one automatically and sends your message once it's ready.