docs(userEvent): Update api-keyboard.mdx (#1308)

Author: neaumusic

docs/user-event/api-keyboard.mdx

@@ -16,7 +16,7 @@ Keystrokes can be described:
   ```js
   keyboard('foo') // translates to: f, o, o
   ```
-  The brackets `{` and `[` are used as special characters and can be referenced
+  The opening brackets `{` and `[` are used as special characters and can be referenced
   by doubling them.
   ```js
   keyboard('{{a[[') // translates to: {, a, [
@@ -35,7 +35,7 @@ Keystrokes can be described:
   prefixing them with a backslash `\`.
 
   ```js
-  keyboard('{\}}') // translates to: }
+  keyboard('{\\}}') // translates to: }
   ```
 
 - Per