Add some simple scripts for signing/flashing

These are some simple scripts for signing images (with an example with a
hardcoded path), a fixed root key that matches the one checked into the
code, and a few scripts to use the Segger debugger to flash the images.
diff --git a/root.pem b/root.pem
new file mode 100644
index 0000000..78c0c34
--- /dev/null
+++ b/root.pem
@@ -0,0 +1,27 @@
+-----BEGIN RSA PRIVATE KEY-----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+-----END RSA PRIVATE KEY-----