Pointed LM Docs at expected keycodes (#4835)

* Pointed LM Docs at expected keycodes

* Update docs/feature_advanced_keycodes.md

Co-Authored-By: germ <jeremythegeek@gmail.com>

docs/feature_advanced_keycodes.md

@@ -25,7 +25,7 @@ These functions allow you to activate layers in various ways. Note that layers a
 
 * `DF(layer)` - switches the default layer. The default layer is the always-active base layer that other layers stack on top of. See below for more about the default layer. This might be used to switch from QWERTY to Dvorak layout. (Note that this is a temporary switch that only persists until the keyboard loses power. To modify the default layer in a persistent way requires deeper customization, such as calling the `set_single_persistent_default_layer` function inside of [process_record_user](custom_quantum_functions.md#programming-the-behavior-of-any-keycode).)
 * `MO(layer)` - momentarily activates *layer*. As soon as you let go of the key, the layer is deactivated. 
-* `LM(layer, mod)` - Momentarily activates *layer* (like `MO`), but with modifier(s) *mod* active. Only supports layers 0-15 and the left modifiers.
+* `LM(layer, mod)` - Momentarily activates *layer* (like `MO`), but with modifier(s) *mod* active. Only supports layers 0-15 and the left modifiers: `MOD_LCTL`, `MOD_LSFT`, `MOD_LALT`, `MOD_LGUI` (note the use of `MOD_` constants instead of `KC_`). These modifiers can be combined using bitwise OR, e.g. `LM(_RAISE, MOD_LCTL | MOD_LALT)`.
 * `LT(layer, kc)` - momentarily activates *layer* when held, and sends *kc* when tapped. Only supports layers 0-15.
 * `OSL(layer)` - momentarily activates *layer* until the next key is pressed. See [One Shot Keys](#one-shot-keys) for details and additional functionality.
 * `TG(layer)` - toggles *layer*, activating it if it's inactive and vice versa