Add docusaurus headers to markdown files in the docs directory

[JohnMcW]

We copy the markdown files from this library's docs directory into this repo:

https://github.com/apache/incubator-milagro/tree/develop/docs/cryptojs

Then use Docusaurus to build the Milagro website here:

http://milagro.apache.org/docs/amcl-javascript-api/

However, Docusaurus requires that each md file has a header in the following format:

---
id: aes
title: AES
sidebar_label: AES
---

(this is for aes.md)

Please can you add these headers in this repo so that they don't have to be added manually each time we need to update the docs site?