doc: Bring in the FIT examples

Convert these to rST format and add them to the index.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/usage/fit/sign-configs.rst b/doc/usage/fit/sign-configs.rst
new file mode 100644
index 0000000..6a3df8f
--- /dev/null
+++ b/doc/usage/fit/sign-configs.rst
@@ -0,0 +1,52 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Signed configurations
+=====================
+
+::
+
+    /dts-v1/;
+
+    / {
+        description = "Chrome OS kernel image with one or more FDT blobs";
+        #address-cells = <1>;
+
+        images {
+            kernel {
+                data = /incbin/("test-kernel.bin");
+                type = "kernel_noload";
+                arch = "sandbox";
+                os = "linux";
+                compression = "lzo";
+                load = <0x4>;
+                entry = <0x8>;
+                kernel-version = <1>;
+                hash-1 {
+                    algo = "sha1";
+                };
+            };
+            fdt-1 {
+                description = "snow";
+                data = /incbin/("sandbox-kernel.dtb");
+                type = "flat_dt";
+                arch = "sandbox";
+                compression = "none";
+                fdt-version = <1>;
+                hash-1 {
+                    algo = "sha1";
+                };
+            };
+        };
+        configurations {
+            default = "conf-1";
+            conf-1 {
+                kernel = "kernel";
+                fdt = "fdt-1";
+                signature {
+                    algo = "sha1,rsa2048";
+                    key-name-hint = "dev";
+                    sign-images = "fdt", "kernel";
+                };
+            };
+        };
+    };