Resolve "Write API documentation"

Closes #2 (closed)

docs/api_documentation.rst

@@ -33,7 +33,7 @@ Encryption keys:
   Add a new password to a new Luks slot.
 
   Post data: ``{"password": password, "new-password": new-password}``
-``POST /encryption/keys/{slot-id}``
+``PUT /encryption/keys/{slot-id}``
   Change a luks slot's password. {slot} corresponds to a slot id listed by ``GET
   /encryption/keys``.