fix(uxm_setup.turn_on_fixed_tones): Docstring.

sodetlib/operations/uxm_setup.py

@@ -472,8 +472,22 @@ def setup_fixed_tones(
     return fixed_tones
 
 
-# TODO does this work even without a call to `tracking_setup`?
+@sdl.set_action()
 def turn_on_fixed_tones(S, cfg, band):
+    """
+    Read fixed tones from the device config and ensure the corresponding channels
+    are set to the specified amplitude and have feedback disabled.
+
+    Args
+    ----
+    S : SmurfControl
+        Pysmurf instance
+    cfg : DetConfig
+        DetConfig instance
+    band : int
+        The band to operate on.
+    """
+
     # try to read from config
     try:
         foff = cfg.dev.bands[band]["fixed_tones"]["freq_offsets"]