docs: Fix the typo for imgtool keygen command

Signed-off-by: Harry Jiang <explora26@gmail.com>
diff --git a/docs/encrypted_images.md b/docs/encrypted_images.md
index 4bc7f86..74443db 100644
--- a/docs/encrypted_images.md
+++ b/docs/encrypted_images.md
@@ -141,7 +141,7 @@
 
 ## [Creating your keys with imgtool](#creating-your-keys-with-imgtool)
 
-`imgtool` can generate keys by using `imgtool genkey -k <output.pem> -t <type>`,
+`imgtool` can generate keys by using `imgtool keygen -k <output.pem> -t <type>`,
  where type can be one of `rsa-2048`, `rsa-3072`, `ecdsa-p256`, `ecdsa-p224`
 or `ed25519`. This will generate a keypair or private key.