Add extensions/keys page

Author: dacap

customization.md

@@ -10,8 +10,9 @@ some file (extensions or script) and installing it from *Edit >
 Preferences > Extensions* or *File > Scripts > Open Scripts Folder*:
 
 * [Extensions](extensions.md)
-  * [Language](language.md)
-  * [Themes](themes.md)
+  * [Keys](extensions/keys.md)
+  * [Language](extensions/language.md)
+  * [Themes](extensions/themes.md)
 * [Scripting](scripting.md)
 
 ---

extensions.md

@@ -27,6 +27,7 @@ file inside: the `package.json` file.
 
 The structure of a `.aseprite-extension` file depends on the kind of extension:
 
+* [Keys](extensions/keys.md)
 * [Palettes](extensions/palettes.md)
 * [Languages](extensions/languages.md)
 * [Themes](extensions/themes.md)

extensions/keys.md

@@ -0,0 +1,54 @@
+# Keys
+
+Since **Aseprite v1.2.35** you can create extensions with keyboard
+shortcuts.  The content of a `.aseprite-extension` file for an
+extension with keyboard shorcuts should be something like this:
+
+```
+keys-example.aseprite-extension
+|
++-- package.json
+|
++-- my-keys.aseprite-keys
+```
+
+Content of `package.json`:
+
+```
+{
+  "name": "my-keys-example",
+  "displayName": "My Keys Example",
+  "description": "Keys to do something",
+  "version": "1.0",
+  "author": { "name": "Full Name", "url": "https://twitter.com/your_username_or_homepage_url" },
+  "categories": [
+    "Keys"
+  ],
+  "contributes": {
+    "keys": [
+      { "id": "my-keys", "path": "./my-keys.aseprite-keys" }
+    ]
+  }
+}
+```
+
+**Example** content of `my-keys.aseprite-keys` (a file similar to
+[user.aseprite-keys](https://www.aseprite.org/docs/files/#useraseprite-keys)
+in the [Preferences folder](https://www.aseprite.org/docs/preferences/) that
+can be created / exported from [Edit > Keyboard Shortcuts](keyboard-shortcuts.md)):
+
+```
+<?xml version="1.0" encoding="utf-8" ?>
+<keyboard version="1">
+    <commands>
+        <key command="Options" shortcut="J" />
+        <key command="KeyboardShortcuts" shortcut="K" />
+    </commands>
+</keyboard>
+```
+
+---
+
+**SEE ALSO**
+
+[Extensions](extensions.md)