docs(fuzz): Adding fuzzing documentation

Initial fuzzing documentation added. Demonstrates the concept
and usage of the SMC fuzzing tool incorporated into TF-A tests.

Change-Id: Iefda90c108ded205edcd7665d40855ab19b4d475
Signed-off-by: Mark Dykes <mark.dykes@arm.com>
diff --git a/docs/index.rst b/docs/index.rst
index 7e54db2..8c1536e 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -13,6 +13,7 @@
    implementing-tests
    porting/index
    plat/index
+   fuzzing/index
    change-log
    license