ENH: add neuromag and ctf to the builtin standard montages

Author: contsili

mne/channels/montage.py

@@ -186,6 +186,15 @@ class _BuiltinStandardMontage:
         name="brainproducts-RNP-BA-128",
         description="Brain Products with 10-10 electrode names (128 channels)",
     ),
+    _BuiltinStandardMontage(
+        name="ctf275",
+        description="CTF system with 275 sensors (275 axial gradiometers)",
+    ),
+    _BuiltinStandardMontage(
+        name="neuromag306",
+        description="Neuromag system with 306 sensors (204 gradiometers, "
+        "102 magnetometers)",
+    ),
 ]