Added OSL to list of layer toggles

docs/feature_advanced_keycodes.md

@@ -27,6 +27,7 @@ These functions allow you to activate layers in various ways. Note that layers a
 * `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.
 * `LT(layer, kc)` - momentarily activates *layer* when held, and sends *kc* when tapped.
+* `OSL(layer)` - momentarily activates *layer* until the next key is pressed.
 * `TG(layer)` - toggles *layer*, activating it if it's inactive and vice versa
 * `TO(layer)` - activates *layer* and de-activates all other layers (except your default layer). This function is special, because instead of just adding/removing one layer to your active layer stack, it will completely replace your current active layers, uniquely allowing you to replace higher layers with a lower one. This is activated on keydown (as soon as the key is pressed).
 * `TT(layer)` - Layer Tap-Toggle. If you hold the key down, *layer* is activated, and then is de-activated when you let go (like `MO`). If you repeatedly tap it, the layer will be toggled on or off (like `TG`). It needs 5 taps by default, but you can change this by defining `TAPPING_TOGGLE` -- for example, `#define TAPPING_TOGGLE 2` to toggle on just two taps.