Add missing snippet for sign/cwiseSign functions.
diff --git a/doc/snippets/Cwise_sign.cpp b/doc/snippets/Cwise_sign.cpp
new file mode 100644
index 0000000..49920e4
--- /dev/null
+++ b/doc/snippets/Cwise_sign.cpp
@@ -0,0 +1,2 @@
+Array3d v(-3,5,0);
+cout << v.sign() << endl;