chore(docs): fix markdown

Author: saibatizoku

rust/signed_doc/README.md

@@ -13,14 +13,16 @@ Catalyst signed document crate implementation based on this
 openssl genpkey -algorithm=ED25519 -out=private.pem -outpubkey=public.pem
 ```
 
-### Prepare non-signed document,
+### Prepare non-signed document
+
 `meta.json` file should follow the [`meta.schema.json`](./meta.schema.json).
 
 ```shell
 cargo run -p catalyst-signed-doc --example mk_signed_doc build signed_doc/doc.json signed_doc/doc.cose signed_doc/meta.json
 ```
 
 ### Sign document
+
 `KID` is a valid Catalyst ID URI.
 
 ```shell