docs: add is_exec and is_sticky to Cha (#54)

docs/plugins/types.md

@@ -19,6 +19,8 @@ Cha means one file's characteristics with the following properties:
 - `is_char_device` - Whether this file is a character device
 - `is_fifo` - Whether this file is a fifo
 - `is_socket` - Whether this file is a socket
+- `is_exec` - Whether this file is executable
+- `is_sticky` - Whether this file has the sticky bit set
 - `length` - The length of this file, returns an integer representing the size in bytes. Note that it can't reflect the size of a directory, use [`size()`](#app-data.folder-file) instead
 - `created` - The created time of this file in Unix timestamp, or `nil` if it doesn't have a valid time
 - `modified` - The modified time of this file in Unix timestamp, or `nil` if it doesn't have a valid time