docs: List all image elements currently supported by the fuzzer

Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Maria Kustova <maria.k@catit.be>
Message-id: cb71485d0f55d1d8401eebaead8324eb78673060.1408450493.git.maria.k@catit.be
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

docs/image-fuzzer.txt

@@ -125,7 +125,8 @@ If a fuzzer configuration is specified, then it has the next interpretation:
     will be always fuzzed for every test. This case is useful for regression
     testing.
 
-For now only header fields, header extensions and L1/L2 tables are generated.
+The generator can create header fields, header extensions, L1/L2 tables and
+refcount table and blocks.
 
 Module interfaces
 -----------------