Add info about ssh-keygen

README.md

@@ -5,6 +5,9 @@
 Provides SSH signature parser and verifier for
 [SSH file signatures](https://www.agwa.name/blog/post/ssh_signatures).
 
+SSH signatures allow signing arbitrary files and can be used for
+[signing git commits and tags](https://blog.dbrgn.ch/2021/11/16/git-ssh-signatures/).
+
 All features are implemented using pure TypeScript and built-in
 [SubtleCrypto](https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto).
 
@@ -14,6 +17,17 @@ are
 this package allows supplying custom `SubtleCrypto` implementation, such as
 [`webcrypto-ed25519`](https://github.com/jacobbubu/webcrypto-ed25519).
 
+## Creating SSH signatures
+
+SSH signatures can be created using [OpenSSH](https://www.openssh.com/)'s
+[`ssh-keygen`](https://man.archlinux.org/man/ssh-keygen.1):
+
+```sh
+ssh-keygen -Y sign -f ~/.ssh/id_ed25519 -n file file_to_sign
+```
+
+This will create a detached signature in the `file_to_sign.sig` file.
+
 ## Supported algorithms
 
 The following algorithms are supported at this time: