Added initial key lock documentation.

docs/_summary.md

@@ -17,6 +17,7 @@
   * [Mouse keys](mouse_keys.md)
   * [Unicode](unicode.md)
   * [Stenography](stenography.md)
+  * [Key Lock](key_lock.md)
 
 * Reference
   * [Glossary](glossary.md)

docs/make_instructions.md

@@ -158,6 +158,10 @@ This enables using the Quantum SYSEX API to send strings (somewhere?)
 
 This consumes about 5390 bytes.
 
+`KEY_LOCK_ENABLE`
+
+This enables [key lock](key_lock.md). This consumes an additional 260 bytes.
+
 ## Customizing Makefile options on a per-keymap basis
 
 If your keymap directory has a file called `Makefile` (note the filename), any Makefile options you set in that file will take precedence over other Makefile options for your particular keyboard.

docs/quantum_keycodes.md

@@ -17,6 +17,7 @@ On this page we have documented keycodes between `0x00FF` and `0xFFFF` which are
 |`FUNC(n)`/`F(n)`|Call `fn_action(n)`|
 |`M(n)`|to call macro n|
 |`MACROTAP(n)`|to macro-tap n idk FIXME|
+|`KC_LOCK`|The [lock key](key_lock.md)|
 
 ## Bootmagic Keycodes