Fix NVStore README file (changed APIs)

Author: David Saada

features/nvstore/README.md

@@ -22,7 +22,8 @@ Each item is kept in an entry containing a header and data, where the header hol
 - get: Get the value of an item, given key.
 - set: Set the value of an item, given key and value.
 - set_once: Like set, but allows only a one time setting of this item (and disables deleting of this item).
-- set_alloc_key: Like set, but allocates a free key (from the non predefined keys).
+- alloc_key: Allocates a free key (from the non predefined keys) to an owner (an owning feature).
+- free_all_keys_by_owner: Free all allocated keys, given an owner.
 - remove: Remove an item, given key.
 - get_item_size: Get the item value size (in bytes).
 - set_max_keys: Set maximal value of unique keys. Overriding the default of NVSTORE_MAX_KEYS. This affects RAM consumption,