bootutil_public: documented module API

document API of the public, shared code module.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
diff --git a/boot/bootutil/src/bootutil_public.c b/boot/bootutil/src/bootutil_public.c
index f8ead32..3c9e204 100644
--- a/boot/bootutil/src/bootutil_public.c
+++ b/boot/bootutil/src/bootutil_public.c
@@ -26,6 +26,16 @@
  * under the License.
  */
 
+/**
+ * @file
+ * @brief Public MCUBoot interface API implementation
+ *
+ * This file contains API implementation which can be combined with
+ * the application in order to interact with the MCUBoot bootloader.
+ * This file contains shared code-base betwen MCUBoot and the application
+ * which controls DFU process.
+ */
+
 #include <string.h>
 #include <inttypes.h>
 #include <stddef.h>