Clarify that wolfBoot_open_image_address expects the passed in img structure to be memset and does not perform the memset itself.

docs/lib.md

@@ -15,7 +15,7 @@ is initialized when `wolfBoot_open_image_address()` is called. The signature is:
 `int wolfBoot_open_image_address(struct wolfBoot_image* img, uint8_t* image)`
 
 
-where `img` is a pointer to a local (uninitialized) structure of type `wolfBoot_image`, and
+where `img` is a pointer to a local (memset but otherwise uninitalized) structure of type `wolfBoot_image`, and
 `image` is a pointer to where the signed image is mapped in memory, starting from the beginning
 of the manifest header.
 

src/image.c

@@ -1270,6 +1270,9 @@ uint32_t wolfBoot_image_size(uint8_t *image)
  *
  * This function opens an image using the provided image address and initializes
  * the wolfBoot_image structure.
+ * Note that this function initializes the members of the wolfBoot_image structure
+ * but does not initialize the structure itself.  It is expected that the wolfBoot_image
+ * struct is memset to 0 before being passed in, with image->hdr optionally set.
  *
  * @param img The pointer to the wolfBoot_image structure to be initialized.
  * @param image The pointer to the image address.