Updated Note style guide (markdown)

Note-style-guide.md

@@ -16,6 +16,7 @@ Here are some rough guidelines to Rust style. They are followed unevenly and the
 * Constructors are methods called `new` or `new_with_more_details`.
 * Constructors that simply convert from another type are methods called `from_foo`.
 * When writing a binding to an external library, put the raw C bindings in a module called `ffi` (rather than `ll`). Do not create high-level bindings called `hl`.
+* lifetime names are lowercase and are often simply 'a
 
 ## Trait naming