qmp: Documentation for BLOCK_IMAGE_CORRUPTED

Add an appropriate entry describing this event and its parameters into
qmp-events.txt.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

QMP/qmp-events.txt

@@ -18,6 +18,28 @@ Example:
     "data": { "actual": 944766976 },
     "timestamp": { "seconds": 1267020223, "microseconds": 435656 } }
 
+BLOCK_IMAGE_CORRUPTED
+---------------------
+
+Emitted when a disk image is being marked corrupt.
+
+Data:
+
+- "device": Device name (json-string)
+- "msg":    Informative message (e.g., reason for the corruption) (json-string)
+- "offset": If the corruption resulted from an image access, this is the access
+            offset into the image (json-int)
+- "size":   If the corruption resulted from an image access, this is the access
+            size (json-int)
+
+Example:
+
+{ "event": "BLOCK_IMAGE_CORRUPTED",
+    "data": { "device": "ide0-hd0",
+        "msg": "Prevented active L1 table overwrite", "offset": 196608,
+        "size": 65536 },
+    "timestamp": { "seconds": 1378126126, "microseconds": 966463 } }
+
 BLOCK_IO_ERROR
 --------------