Update wfs-referencing.ipynb

lmb -> wavelength

Author: fs446

doc/examples/wfs-referencing.ipynb

@@ -33,8 +33,8 @@
     "\n",
     "xs = -4, 0, 0  # point source on negative x-axis\n",
     "normalize_gain = 4 * np.pi * np.linalg.norm(xs)\n",
-    "lmb = 1 / 4  # m\n",
-    "f = sfs.default.c / lmb  # Hz\n",
+    "wavelength = 1 / 4  # m\n",
+    "f = sfs.default.c / wavelength  # Hz\n",
     "omega = 2 * np.pi * f  # rad/s"
    ]
   },