Add basic layer behavior docs.

docs/docs/behavior/layers.md

@@ -0,0 +1,41 @@
+---
+title: Layers
+---
+
+## Summary
+
+Often, you may want a certain key position to alter which layers are enabled, change the default layer, etc.
+Some of those behaviors are still in the works; the ones that are working now are documented here.
+
+## Defines To Refer To Layers
+
+When working with layers, you may have several different key positions with bindings that enable/disable those layers.
+To make it easier to refer to those layers in your key bindings, and to change which layers are where later, you can
+add a set of `#define`s at the top of your keymap file, and use those layer in your keymap.
+
+For example, if you have three layers, you can add the following to the top of your keymap:
+
+```
+#define DEFAULT 0
+#define LOWER   1
+#define RAISE   2
+```
+
+This allows you to use those defines, e.g. `LOWER` later in your keymap.
+
+## Momentary Layer
+
+The "momentary layer" behavior allows you to enable a layer while a certain key is pressed. Immediately upon
+activation of the key, the layer is enabled, and immediately open release of the key, the layer is disabled
+again.
+
+### Behavior Binding
+
+- Reference: `&mo`
+- Parameter: The layer number to enable/disable, e.g. `1`
+
+Example:
+
+```
+&mo LOWER
+```

docs/sidebars.js

@@ -7,7 +7,7 @@ module.exports = {
       "feature/encoders",
       "feature/underglow",
     ],
-    Behaviors: ["behavior/key-press"],
+    Behaviors: ["behavior/key-press", "behavior/layers"],
     Development: [
       "dev-clean-room",
       "dev-setup",