feat(docs): Add docs for key toggle behavior

docs/docs/behaviors/key-toggle.md

@@ -0,0 +1,26 @@
+---
+title: Key Toggle Behavior
+sidebar_label: Key Toggle
+---
+
+## Summary
+
+The key toggle behavior toggles the press of a key.
+If the key is not currently pressed, key toggle will press it, holding it until the key toggle is pressed again or the key is released in some other way.
+If the key _is_ currently pressed, key toggle will release it.
+
+Example uses for key toggle include shift lock, or `ALT-TAB` window switching without holding down the `ALT` modifier.
+
+### Behavior Binding
+
+- Reference: `&kt`
+- Parameter: The [keycode](../codes/index.mdx), e.g. `LALT` or `DOWN_ARROW`
+
+Example:
+
+```
+&kt LALT
+```
+
+You can use any keycode that works for `&kp` as parameter to `&kt`, however, [modified keys](../codes/modifiers.mdx#modifier-functions) such as `LA(A)` will be toggled based on the status of the base keycode (in this case `A`).
+In other words, modifiers are ignored when determining whether or not the key is currently pressed.

docs/sidebars.js

@@ -28,6 +28,7 @@ module.exports = {
       "behaviors/mod-tap",
       "behaviors/mod-morph",
       "behaviors/macros",
+      "behaviors/key-toggle",
       "behaviors/sticky-key",
       "behaviors/sticky-layer",
       "behaviors/tap-dance",