Document type directive

* doc/snippet-development.org: Add type to directive list.

doc/snippet-development.org

@@ -169,6 +169,15 @@ This binding will be recorded in the keymap =html-mode-map=. To expand a
 paragraph tag newlines, just press =C-u C-c C-c C-m=. Omitting the =C-u=
 will expand the paragraph tag without newlines.
 
+** =# type:= snippet or command
+
+If the =type= directive is set to =command=, the body of the snippet
+is interpreted as lisp code to be evaluated when the snippet is
+triggered.
+
+If it's =snippet= (the default when there is no =type= directive), the
+snippet body will be parsed as described below, in [[Template Syntax]].
+
 ** =# uuid:= unique identifier
 
 Loading a second snippet file with the same uuid would replace the
@@ -179,7 +188,7 @@ previous snippet.
 This is optional and has no effect whatsoever on snippet functionality,
 but it looks nice.
 
-* Template syntax
+* <<Template syntax>>
 
 The syntax of the snippet template is simple but powerful, very similar
 to TextMate's.