core: add description of struct shdr_bootstrap_ta

Adds a description of the fields in struct shdr_bootstrap_ta.

Reviewed-by: Jerome Forissier <jerome@forissier.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/core/include/signed_hdr.h b/core/include/signed_hdr.h
index 5294f43..d75dc87 100644
--- a/core/include/signed_hdr.h
+++ b/core/include/signed_hdr.h
@@ -53,6 +53,11 @@
 #define SHDR_GET_HASH(x)	(uint8_t *)(((struct shdr *)(x)) + 1)
 #define SHDR_GET_SIG(x)		(SHDR_GET_HASH(x) + (x)->hash_size)
 
+/**
+ * struct shdr_bootstrap_ta - bootstrap TA subheader
+ * @uuid:	UUID of the TA
+ * @ta_version:	Version of the TA
+ */
 struct shdr_bootstrap_ta {
 	uint8_t uuid[sizeof(TEE_UUID)];
 	uint32_t ta_version;